Apparatus for pulling single crystal by CZ method

ABSTRACT

In a Czochralski (CZ) single crystal puller equipped with a cooler and a thermal insulation member, which are to be disposed in a CZ furnace, smooth recharge and additional charge of material are made possible. Further, elimination of dislocations from a silicon seed crystal by use of the Dash&#39;s neck method can be performed smoothly. To these ends, there is provided a CZ single crystal puller, wherein a cooler and a thermal insulation member are immediately moved upward away from a melt surface during recharge or additional charge of material or during elimination of dislocations from a silicon seed crystal by use of the Dash&#39;s neck method.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for pulling single crystalby Czochralski (CZ) method (a Czochralski (CZ) single crystal puller)equipped with a cooler for cooling a pulled single crystal.

Further, the present invention relates to a CZ single crystal pullerwhich is equipped with a cooler for cooling a pulled single crystal andwhich can smoothly eliminate dislocations from a silicon seed crystal bymeans of the Dash's neck method.

The present invention also relates to a CZ single crystal puller whichis equipped with a cooler for cooling a pulled single crystal and whichcan smoothly perform recharging and additional charging operations.

The present invention further relates to a CZ single crystal pullerwhich is equipped with a cooler for cooling a pulled single crystal anda safety mechanism for avoiding hazard, which would result frominstallation of the cooler.

The present invention further relates to a technique for optimizingrequirements for manufacturing a silicon wafer to be produced by theCzochralski (CZ) method.

2. Related Art

As a CZ single crystal puller which pulls a single crystal by means ofthe Czochralski (CZ) method, a CZ single crystal puller equipped with acooler to be disposed in a CZ furnace (hereinafter often called a“furnace cooler”) for cooling a pulled single crystal has recently beenemployed. Use of such a CZ single crystal puller equipped with a furnacecooler enables a considerable increase in a single-crystal pull rate.Consequently, efficiency in production of a single crystal ingot orwafer can be increased. Hence, the CZ single crystal puller equippedwith a furnace cooler is of great significance.

Studies conducted by the present inventors showed that presence of acooler poses difficulty in eliminating dislocations from a silicon seedcrystal when an attempt is made to eliminate dislocations (primarilydislocations induced by thermal shock when a seed crystal is immersed ina melt) from a silicon seed crystal through use of the Dash's neckmethod (W. Dash: Journal of Applied Physics 30 (1959) pg. 459).

The present invention has been conceived in light of the foregoingdrawbacks, and a first object of the present invention is to provide aCZ single crystal puller which is equipped with a cooler to be disposedin a CZ furnace and which can smoothly eliminate dislocations from asilicon seed crystal by means of the Dash's neck method.

In addition to the furnace cooler, a thermal insulation shield or a likemember for shielding heat radiating from a heater or a melt is oftendisposed within the CZ furnace in order to optimize requirements forpulling a single crystal.

At the time of pulling of a single crystal through use of the CZ method,material is additionally charged or recharged in order to produce asingle crystal of maximum size during a single process.

However, members to be disposed within a furnace (hereinafter oftencalled “furnace members”); particularly, the cooler and the thermalinsulation shield, hinder additional charge or recharge of material.Great attention must be paid to a problem of melt splashes;particularly, during additional charge or recharge of material, ratherthan during initial charge of material. When a cooler is disposed near acrucible, heating must be effected so as to overcome the cooling effectof the cooler at the time of charge of material. Hence, the amount ofenergy dissipation is increased.

The present invention has been conceived in view of the above-describeddrawbacks, and a second object of the present invention is to provide aCZ single crystal puller which is equipped with a cooler and athermal-insulation shield, both being provided in a CZ furnace, andwhich can smoothly perform additional charge or recharge of material.

In connection with a CZ single crystal puller which pulls a singlecrystal by means of the Czochralski (CZ) method, there have already beenput forward various types of coolers to be disposed in a CZ furnace ofthe CZ single crystal puller. One of the proposed coolers moves withinthe CZ furnace (as described in Japanese Patent Application Laid-OpenNo. 92272/1999). There is room for improving such a furnace cooler.

The present invention has been conceived in view of the drawback setforth, and a third object of the present invention is to provide a CZsingle crystal puller having a cooler which is to be disposed in a CZfurnace and has improved functionality.

A fourth object of the present invention is to provide a CZ singlecrystal puller which has a cooler moving within a CZ furnace and asafety mechanism, wherein the cooler located within the CZ furnaceimmediately avoids hazards by means of appropriately detecting potentialcollision with other furnace members.

In connection with a silicon wafer produced by means of the CZ methodfor use in manufacturing semiconductor devices, crystallineimperfections which deteriorate the quality of a device are present inthe surface layer of a silicon wafer that is simply sliced off from asilicon ingot. As the silicon wafer is subjected to intense heattreatment (i.e., annealing), voids existing in the surface layer of awafer disappear. For example, it has been known that voids—which Aredetected as, for example, LSTDs, FPDs, or COPs, and exist in the surfacelayer of a CZ silicon wafer having been subjected to hydrogen heattreatment (hydrogen annealing)-disappear and as a result the waferexhibits a superior oxide film withstand-pressure characteristic (asdescribed in Japanese Patent Publication No. 80338/1991).

However, the effect of hydrogen annealing is limited to solely the areain the vicinity of the uppermost surface of a silicon wafer. In thisregard, the present inventors found that the rate at or depth to whichdefects located in the vicinity of the surface layer of a wafer areeliminated by means of high-temperature annealing substantially dependson the sizes of initial defects. The present inventors have proposed amethod of expanding a defect-free area from the surface layer of a waferto a comparatively deep position in the wafer, by means of increasing acooling rate of crystal being grown within a temperature zone in whichdefects are apt to arise (as described in Japanese Patent ApplicationLaid-Open No. 208987/1998), controlling a V/G (V denotes a pull rate,and G denotes a temperature gradient along the crystallographic axis andin the vicinity of a melting point), or controlling the diameter of anOSF ring (as described in Japanese Patent Application Laid-Open No.154095/2000), thus miniaturizing size of defects in a crystal.

So long as a rate at which a crystal is to be pulled (hereinafter calledsimply a “crystal pull rate”) is increased, the method enablesminiaturization of defects of a growing crystal to a size at which thedefects are apt to disappear by means of annealing. Further, if the pullrate is increased, the volume of silicon ingot produced per unit time iseventually increased, thus improving the production efficiency of awafer.

If a crystal can be pulled faster than what has been expected thus far,the production efficiency of wafers of all types can be improved to amuch greater extent, regardless of whether the wafer is to be used forepitaxial growth or annealing purpose.

In a case where a crystal pull rate is increased, if miniaturization ofcrystalline imperfections becomes possible at least without a crystalbeing adversely affected by an increase in pull rate, crystallineimperfections can be miniaturized at a high pull rate. Particularly, ifan increase in pull rate and miniaturization of crystallineimperfections can be attained simultaneously, immediate production of awafer for annealing purpose (i.e., from which crystalline imperfectionsare likely to disappear and which is suitable for undergoing annealing)can be attained.

The present invention has been conceived in view of the drawbacks of therelated art set forth, and a fifth object of the present invention is toimprove production efficiency of wafers of all types, regardless ofwhether or not the wafers are to be used for epitaxial growth orannealing purpose, by means of increasing the crystal pull rate.

A sixth object of the present invention is to simultaneous realizationof miniaturization of crystalline imperfections to a size smaller thanhas been expected thus far and an increased pull rate, thereby improvingthe production efficiency of a wafer for annealing purpose.

SUMMARY OF THE INVENTION

To achieve the first object, the present invention provides aCzochralski (CZ) single crystal puller, in which a cooler is moved awayfrom a melt surface during the course of elimination of dislocationsfrom a silicon seed crystal using the Dash's neck method.

The studies conducted by the present inventors show that, when a thermalinsulation member is disposed at a position above a melt surface and acooling coil is disposed at a position much higher than the location ofthe thermal insulation member, dislocations can be eliminated only underspecific conditions to which the Dash's neck method is applied. Thestudies have greatly contributed to completion of the present invention.

A technique analogous to the present invention is described in JapanesePatent Application Laid-Open No. 189488/1999. The application statesthat elimination of dislocations can be achieved without involvement ofa necking process, by means of setting the distance between a meltsurface and the lower end of the thermal insulation member to apredetermined range, and reducing the temperature difference between amelt and a seed crystal before immersion into the melt. However, if acooler is located in the vicinity of a seed crystal, elimination ofdislocations is impossible. Examples of inventions in which coolingmeans is placed at a position higher than a melt for cooling crystal aredescribed in Japanese Patent Application Laid-Open Nos. 317491/1992 and239291/1996. However, elimination of dislocations after a seed crystalhas been immersed in melt is not described at all.

More specifically, in order to achieve the first object, the presentinvention provides:

(A1) A method of enabling adjustment for eliminating defects by use ofthe Dash's neck method, by means of arranging a cooler for cooling apulled single crystal provided in a Czochralski (CZ) single crystalpuller so as to be able to move within a CZ furnace.

(A2) A method of enhancing the efficiency of eliminating dislocation byuse of the Dash's neck method, by means of moving away from a siliconmelt surface a cooler which cools a pulled single crystal and isdisposed in a CZ silicon single crystal puller so as to be movablewithin a CZ furnace, during the course of drawing of a seed by use ofthe Dash's neck method.

(A3) The method as defined in (A2) is characterized in that a thermalinsulation member is moved away from a silicon melt surface along withthe cooler.

In the present invention, during the course of drawing of a seed by useof the Dash's neck method, a cooler and a thermal insulation member arebasically spaced apart from the surface of a silicon melt. The locationsto which the cooler and the thermal insulation member are retracted arelocations where the cooler or the thermal insulation member do notadversely affect elimination of dislocations. Most preferably, thelocations belong to a “dislocation-elimination range” (as will bedescribed by reference to the accompanying drawings in a subsequentembodiment, the range can be taken as a given range mapped by thedistance between the melt surface and the lower end of the cooler and bythe distance between the melt surface and the lower end of the thermalinsulation member). When the cooler and the thermal insulation memberare situated in the range, there is yielded the same effect as thatyielded when the cooler and the thermal insulation member are notprovided in the CZ furnace (i.e., the effect of eliminating dislocationsby virtue of the Dash's neck method).

(A4) A method of removing a cooler for cooling a pulled single crystalwhich is disposed in a CZ silicon single crystal puller, for the purposeof enhancing the efficiency of elimination of dislocations by use of theDash's neck method.

(A5) A Czochralski (CZ) single crystal puller having a cooler forcooling a pulled single crystal, and a hoisting-and-lowering apparatusfor hoisting or lowering the cooler within a CZ furnace, wherein

-   -   the hoisting-and-lowering apparatus hoists the cooler to a        higher position during the course of drawing of a seed according        to the Dash's neck method.

(A6) A Czochralski (CZ) single crystal puller having a cooler forcooling a pulled single crystal, a hoisting-and-lowering apparatus forhoisting or lowering the cooler within a CZ furnace, and a thermalinsulation member which surrounds a single crystal and is disposed inthe CZ furnace in a portable manner, wherein

-   -   the hoisting-and-lowering apparatus hoists the cooler and the        thermal insulation member to higher positions during the course        of drawing of a seed according to the Dash's neck method.

(A7) The CZ single crystal puller as defined (A6) is characterized inthat the cooler is provided with an engagement member and the thermalinsulation member is provided with another engagement member and that,when the cooler is hoisted, the engagement members are engaged with eachother, and the thermal insulation member is lifted in association withupward movement of the cooler.

(A8) A Czochralski (CZ) single crystal puller having a crucible which isfreely movable in the vertical direction and stores silicon melt and acooler for cooling a pulled single crystal, wherein

-   -   a seed is drawn by use of the Dash's neck method while the        crucible is lowered and the cooler is moved away from the        surface of the silicon melt.

(A9) A Czochralski (CZ) single crystal puller having a crucible which isfreely movable in the vertical direction and stores silicon melt, acooler for cooling a pulled single crystal, and a thermal insulationmember for surrounding a silicon single crystal pulled from the siliconmelt, wherein

-   -   a seed is drawn by use of the Dash's neck method while the        crucible is lowered and while the cooler and the bottom surface        of the thermal insulation member are moved away from the surface        of the silicon melt.

(A10) A silicon ingot produced by the CZ single crystal puller asdefined in any one of (A5) to (A9).

(A11) A silicon wafer sliced off from the silicon ingot defined in(A10).

When a wafer is sliced off from a silicon ingot, a wafer is usuallysliced off from an area on the silicon ingot to be used for producingproducts. In contrast, when a wafer is sliced for research purpose or asa dummy, there may be a case where a wafer is sliced off from a shoulderor tail portion of the silicon ingot.

To achieve the second object, the present invention provides aCzochralski (CZ) single crystal puller, wherein a cooler and a thermalinsulation member are immediately moved upward away from a melt surfaceat the time of additional charge or recharge of material.

More specifically, in order to achieve the second object, the presentinvention provides:

(B1) A method of promoting smooth recharge or additional charge ofmaterial, by means of arranging a crucible for melting charged materialand a cooler for cooling a pulled single crystal disposed in aCzochralski (CZ) single crystal puller such that the crucible and thecooler are movable within a CZ furnace.

(B2) A Czochralski (CZ) single crystal puller for recharge or additionalcharge purpose, comprising:

-   -   a crucible for melting charged material;    -   a cooler for cooling a pulled single crystal; and    -   a hoisting-and-lowering apparatus for hoisting or lowering the        cooler within a CZ furnace.

(B3) A Czochralski (CZ) single crystal puller for recharge or additionalcharge purpose, comprising:

-   -   a crucible for melting charged material;    -   a cooler for cooling a pulled single crystal; and    -   a hoisting-and-lowering apparatus for hoisting or lowering the        cooler within a CZ furnace, wherein the hoisting-and-lowering        apparatus hoists the cooler so as to move away from material        when material is charged.

(B4) The CZ single crystal puller as defined in (B3) further comprises athermal insulation member which surrounds a single crystal and isdisposed in the CZ furnace in a portable manner, wherein the cooler isprovided with an engagement member, and the thermal insulation member isprovided with another engagement member; and wherein, when the cooler ishoisted, the engagement members are engaged with each other, and thethermal insulation member is lifted in association with upward movementof the cooler.

The expression “portable state” means that setting are made such thatthe thermal insulation member is freely removable and can be movedwithin the furnace.

(B5) The CZ single crystal puller as defined in (B3) or (B4) ischaracterized in that a CZ single crystal puller is used for rechargingor additional charging purpose.

(B6) The CZ single crystal puller as defined in any one of (B2) through(B5) is characterized in that the cooler is a water-cooling type coolerincluding a cooling pipe stack which helically surrounds a singlecrystal and that the engagement member provided in the cooler is a platemember with an engagement section to be inserted into a space betweenthe cooling pipe stack of the cooler.

(B7) The CZ single crystal puller as defined in (B2), (B5), or (B6) ischaracterized in that a heater for heating the crucible is equipped witha side heater disposed at the side of the crucible and a bottom heaterdisposed below the crucible.

(B8) The CZ single crystal puller as defined in (B7) is characterized inthat the output of the side heater or the output of the bottom heater orboth are adjusted in accordance with the amount of melt, as required.

In the CZ single crystal puller according to the present invention, anoutput of at least one of the side heater and the bottom heater isadjusted, as required, in accordance with the level of melt.Particularly, when a melt is diminished, there can be avoided a problemof an increase in the amount of heat applied to the crucible in order toovercome a cooling effect of the cooler.

As a matter of course, a magnetic field can be applied to the cruciblewhile a side heater and a bottom heater are turned on. Further,application of a magnetic field may or may not be effected while onlythe bottom heater is turned on. As means for applying a magnetic fieldto a material melt in the crucible, there can be employed means such asthat described in, for example, Japanese Patent Application Laid-OpenNo. 45889/1981. Further, as means for generating a cusp magnetic field,there can be employed means such as that described in Japanese PatentApplication Laid-Open No. 217493/1983.

(B9) A method of curtailing costs for producing a wafer, by use of a CZsingle crystal puller for recharge or additional charge purpose definedin (B2), (B5), or (B8).

(B10) A silicon ingot produced by a CZ single crystal puller forrecharge or additional charge purpose defined in (B2), (B5), or (B8).

(B11) A silicon wafer sliced off from the silicon ingot defined in(B10).

A silicon ingot manufactured by a CZ single crystal puller for rechargepurpose or a CZ single crystal puller for additional charge purposeaccording to the present invention is longer than that produced by anordinary CZ single crystal puller, by the amount corresponding to thatproduced as a result of recharge or additional charge operation.Further, the CZ single crystal puller according to the present inventionemploys a cooler and enables high-speed pulling of crystal. Hence, theCZ single crystal puller according to the present invention can producea silicon ingot longer than that produced by the ordinary CZ singlecrystal puller during the same period of time in which a silicon ingotis produced by the ordinary CZ single crystal puller. For this reason,manufacturing costs can be reduced from those incurred when a siliconingot is produced by an ordinary CZ silicon crystal puller. Thus, therecan be provided a less-expensive silicon ingot or less-expensive siliconwafers.

In a sense, when a less-expensive silicon ingot or a less-expensivesilicon wafer is provided (particularly when the price of a siliconingot or wafer is far cheaper and cannot be achieved by application ofthe conventional technology), it can be suggested that the silicon ingotor wafer was produced by means of the CZ single crystal puller forrecharge purpose of the CZ single crystal puller for additional purposeaccording to the present invention. Hence, infringement of the right ofthe present invention can be suggested.

When a wafer is sliced off from a silicon ingot, a wafer is usuallysliced off from an area on the silicon ingot to be used for producingproducts. In contrast, when a wafer is sliced for research purpose or asa dummy, there may be a case where a wafer is sliced off from a shoulderor tail portion of the silicon ingot.

The silicon wafer production method and CZ single crystal pulleraccording to the present invention are not affected by the type of asingle crystal ingot to be pulled. It is thought that the method andpuller can be applied to a general CZ method. Hence, a single crystalingot to be pulled is not limited to a silicon single crystal ingot.

To achieve the third object of the present invention, immediateoperation for avoiding hazard is ensured by means of changing the travelspeed of the cooler, as required. The travel direction of the cooler isnot limited to the vertical direction. Directional variations are added,such as movement in an inclined direction or rotation, whereby a cooleris hoisted so as not to hinder movement or visual recognition of otherfurnace members.

More specifically, in order to achieve the third object, the presentinvention provides:

(C1) A Czochralski (CZ) single crystal puller for pulling a singlecrystal from a melt, having a crucible for storing melt, a cruciblehoisting-and-lowering apparatus for hoisting or lowering the crucible, athermal insulation member for surrounding a pulled single crystal, aheater for supplying heat to the crucible, a cooler for cooling thepulled single crystal, and a cooler movement apparatus for moving thecooler, wherein

-   -   the cooler movement apparatus changes a travel speed of the        cooler in two or more steps.

Preferably, the cooler movement apparatus is a coolerhoisting-and-lowering apparatus for moving the cooler vertically.

(C2) A Czochralski (CZ) single crystal puller for pulling a singlecrystal from a melt, having a crucible for storing melt; a cruciblehoisting-and-lowering apparatus for hoisting or lowering the crucible; athermal insulation member for surrounding a pulled single crystal; aheater for supplying heat to the crucible; a cooler for cooling thepulled single crystal; a chamber for storing the crucible, the cruciblehoisting-and-lowering apparatus, the thermal insulation member, theheater, and the cooler; and a cooler movement apparatus for moving thecooler, wherein

-   -   the cooler includes a cooling pipe stack which surrounds a        pulled single crystal, and a supply-and-exhaust pipe which        passes through the chamber and supplies cooling water to the        cooling pipe stack, and    -   the cooler movement apparatus includes a bridging member        connected to the supply-and-exhaust pipe, a screw-threaded shaft        screwed to the bridging member, and a drive member for rotating        the screw-threaded shaft.

(C3) The CZ single crystal puller as defined in (C2) further comprisesan expansion-and-contraction member which covers an area in the chamberthrough which the supply-and-exhaust pipe of the chamber passes suchthat a hermetic state in the chamber is maintained, and expands orcontracts in accordance with vertical movement of the supply-and-exhaustpipe.

(C4) The CZ single crystal puller as defined in (C3) is characterized inthat the cooler hoisting-and-lowering apparatus moves the cooler in thevertical direction.

(C5) The CZ single crystal puller as defined in (C3) is characterized inthat the cooler hoisting-and-lowering apparatus moves the cooler in aninclined direction.

(C6) The CZ single crystal puller as defined in (C5) is characterized inthat a plurality of pieces of cooler hoisting-and-lowering apparatus areprovided in the chamber and that the cooling pipe stack of the cooler isseparated into separated into segments which are to be integrated so asto constitute a cylindrical shape and is equal in number to the coolerhoisting-and-lowering apparatus.

(C7) The CZ single crystal puller as defined in (C4) or (C5) furthercomprises an encoder for tracing a distance over which the cooler isvertically moved.

(C8) The CZ single crystal puller as defined in any one of (C2) through(C7) further comprises a limiter member for hindering lower movement ofthe bridging member from a predetermined position of the screw-threadedshaft.

The simplest limiter member is a solid member such as a metal block.Such a solid member may be formed from a limiter switch (LS). Thebridging member may be returned upward immediately after contact on thelimiter member has been detected.

(C9) The CZ single crystal puller as defined in any one of (C2) through(C8), the cooler hoisting-and-lowering apparatus changes the speed ofvertical movement of the cooler in two steps or more.

The CZ single crystal puller according to the present invention can beprovided with magnetic field application means for applying a magneticfield to a melt of material stored in a crucible. As means for applyinga magnetic field to a material melt in the crucible, there can beemployed means such as that described in, for example, Japanese PatentApplication Laid-Open No. 45889/1981. Further, as means for generating acusp magnetic field, there can be applied means such as that describedin Japanese Patent Application Laid-Open No. 217493/1983.

The silicon wafer production method and CZ single crystal pulleraccording to the present invention are not affected by the type of asingle crystal ingot to be pulled. It is thought that the method andpuller can be applied to a general CZ method. Hence, a single crystalingot to be pulled is not limited to a silicon single crystal ingot.

In order to achieve the fourth object, the present invention provides,as an example, a CZ single crystal puller, in which a touch sensor isformed between a cooler and another member, and collision between thecooler and another member is immediately and accurately detected. On thebasis of the result of detection, the cooler is retracted immediatelyfrom a dangerous location.

More specifically, in order to achieve the fourth object, the presentinvention provides:

(D1) A method of enhancing maintainability of a Czochralski (CZ) singlecrystal puller, by means of arranging a cooler for cooling a pulledsingle crystal provided in the CZ single crystal puller so as to be ableto move within a CZ furnace.

Here, the expression “movement” is abroad concept covering ascendingaction and descending action. The expression implies curved motion, suchas rotational movement, as well as linear motion in the longitudinal,lateral, and slant directions.

(D2) A method of enhancing maintain ability of a Czochralski (CZ) singlecrystal puller equipped with a cooler which can be hoisted and loweredwithin a CZ furnace and cools a pulled single crystal, wherein, in theevent that anomalies have arisen in the CZ single crystal puller, thecooler is retracted from a location where the anomalies have arisen.

It is though that, in most cases, retraction of a cooler from a locationwhere anomalies have arisen is embodied by moving the cooler away from amelt surface or moving the cooler away from a pulled single crystal.

(D3) A method of enhancing maintain ability of a Czochralski (CZ) singlecrystal puller equipped with a cooler which can be hoisted and loweredwithin a CZ furnace and cools a pulled single crystal, wherein, in theevent that anomalies have arisen in the CZ single crystal puller forreasons of vertical movement of the cooler, the cooler is temporarilymoved in the reverse direction.

The expression “temporarily moving the cooler in the reverse direction”means that, if the cooler is in the course of lowering action, thecooler is lifted slightly. In contrast, if the cooler is in the courseof ascending action, the cooler is lowered slightly. In the CZ singlecrystal puller according to the present invention, the upward movementor downward movement of the cooler in this case falls within a range ofabout 5 mm.

(D4) A method of enhancing maintainability of a Czochralski (CZ) singlecrystal puller equipped with a cooler which can be hoisted and loweredwithin a CZ furnace and cools a pulled single crystal, wherein the speedof vertical movement of the cooler is made variable; and wherein, in theevent that anomalies have arisen in the CZ single crystal puller, thecooler is retracted from a location where the anomalies have arisen.

(D5) A method of enhancing maintainability of a Czochralski (CZ) singlecrystal puller equipped with a cooler which can be hoisted and loweredwithin a CZ furnace and cools a pulled single crystal, wherein the speedof vertical movement of the cooler is made variable; and wherein, in theevent that anomalies have arisen in the CZ single crystal puller forreasons of vertical movement of the cooler, the cooler is switched to ahigh-speed mode and is retracted from a location where the anomalieshave arisen.

(D6) The method as defined in any one of (D1) through (D5) ischaracterized in that the cooler is of water-cooling type.

(D7) A Czochralski (CZ) single crystal puller having a cooler forcooling a pulled single crystal and a hoisting-and-lowering apparatusfor hoisting or lowering the cooler within a CZ furnace, wherein, in theevent that anomalies have arisen in the CZ single crystal puller, thehoisting-and-lowering apparatus hoists the cooler so as to move awayfrom a melt surface.

(D8) The CZ single crystal puller as defined in (D7) is characterized inthat the hoisting-and-lowering apparatus variably changes the hoistingor lowering speed of the cooler, and, in the event that anomalies havearisen, the hoisting-and-lowering apparatus is switched to a higherspeed and moves the cooler away from a melt surface.

(D9) The CZ single crystal puller as defined in (D7) or (D8) furthercomprises a thermograph for sensing the distribution of internaltemperature of the CZ furnace or a temperature sensor for sensing thetemperature of the surface of the cooler, wherein, when an anomalousrise in the surface temperature of the cooler is sensed, the cooler ismoved away from a pulled single crystal and material melt.

The “temperature sensor” is essentially provided on the side of thecooler facing a pulled single crystal (i.e., on the interior side of thecooler). However, if the temperature sensor is provided on the exteriorside of the cooler, overheating of the thermal insulation member by theheater disposed outside (i.e., the heater for heating the crucible) canalso be sensed.

(D10) A Czochralski (CZ) single crystal puller having a cooler forcooling a pulled single crystal and a hoisting-and-lowering apparatusfor hoisting or lowering the cooler within a CZ furnace, wherein, in theevent that near miss or collision between the cooler and another furnacemember during the lowering of the cooler is detected, thehoisting-and-lowering apparatus hoists the cooler.

(D11) The Czochralski (CZ) single crystal puller as defined in (D10) ischaracterized in that the hoisting-and-lowering apparatus verticallymoves the cooler at a variable speed and that, in the event that nearmiss or collision has arisen, the hoisting-and-lowering apparatus isswitched to a high speed and hoists the cooler.

(D12) A Czochralski (CZ) single crystal puller having a cooler forcooling a pulled single crystal, a hoisting-and-lowering apparatus forhoisting or lowering the cooler within a CZ furnace, and a range sensorfor sensing the positional relationship between members, wherein, in theevent that near miss or collision between the cooler and pulled singlecrystal or material melt or between other furnace members is detected bythe range sensor, the cooler is retracted from a location where the nearmiss or collision has been detected.

Near miss or collision between a cooler and melt of material can bedetected through use of a so-called melt level sensor (described in,e.g., Japanese Patent Application Laid-Open No. 264779/2000). Further,near miss or collision between a cooler and a pulled single crystalbecomes possible when the “range sensor” is a two-dimensional sensor.The melt level sensor described in the previously-described JapanesePatent Application Laid-Open No. 264779/2000 also has a two-dimensionalsensor function. Hence, the melt level sensor is suitable as a sensor tobe attached to the CZ single crystal puller according to the presentinvention. Here, the two-dimensional sensor includes an embodiment inwhich the horizontal positional relationship is detected by means of aCCD camera.

(D13) A Czochralski (CZ) single crystal puller having a cooler forcooling a pulled single crystal and a hoisting-and-lowering apparatusfor hoisting or lowering the cooler within a CZ furnace, wherein a touchsensor is constituted as a whole between the cooler and pulled singlecrystal or material melt or between other furnace members is detected bythe range sensor; and wherein, when the touch sensor has sensed contact,the cooler is retracted from a location where the contact has beensensed.

Here, the expression “constitutes a touch sensor” means that a cooler isinsulated from a pulled single crystal; for example, a feeble current isapplied to the cooler and crystal while an ammeter is connected to thecooler. Alternatively, a melt of material is insulated from otherfurnace members, and a feeble current is applied to them while anammeter is connected to the furnace members.

(D14) A Czochralski (CZ) single crystal puller having a cooler forcooling a pulled single crystal and a hoisting-and-lowering apparatusfor hoisting or lowering the cooler within a CZ furnace, wherein, in theevent that overload has arisen during the course of vertical movement ofthe cooler, the hoisting-and-lowering apparatus moves the cooler in thedirection opposite to that in which the overload is to arise, therebyretracting the cooler away from the location where the overload hasarisen.

(D15) A Czochralski (CZ) single crystal puller having a cooler forcooling a pulled single crystal and a hoisting-and-lowering apparatusfor hoisting or lowering the cooler within a CZ furnace, wherein, in theevent that anomalous changes have arisen in the weight of a singlecrystal during the course of pulling of the single crystal, the cooleris retracted away from the single crystal.

The mechanism described in (D12) through (D15) can be incorporated intothe puller described in (D10) or (D11).

(D16) The CZ single crystal puller as defined in any one of (D15)through (D17) is characterized in that the cooler is of water-coolingtype.

(D17) The CZ single crystal puller as defined in (D16) further comprisesa steam sensor for sensing steam originating from the CZ furnace,wherein, in the event that the steam sensor detects steam, the cooler ismoved away from a pulled single crystal or material melt.

(D18) The CZ single crystal puller as defined in (D16) further comprisesa thermometer for sensing the temperature of cooling water which hascirculated through the cooler, wherein, in the event that an anomalousarise in the temperature of the cooling water has been detected, thecooler is moved away from a pulled single crystal or material melt.

(D19) A Czochralski (CZ) single crystal puller having a cooler forcooling a pulled single crystal, a hoisting-and-lowering apparatus forhoisting or lowering the cooler within a CZ furnace, and an encoder fortracing a distance over which the cooler has been vertically moved,wherein, in the event that near miss or collision between the cooler andmaterial melt or between other furnace members is detected on the basisof a value computed through use of information output from the encoder,the cooler is retracted from a location where the near miss or collisionis detected.

In order to achieve the fifth object, the present inventors have pinneddown a combination of factors which do not mutually act in a negativemanner (and which preferably a combination of factors which act in apositive manner). By means of such a combination, the crystal pull rateis increased to a speed greater than that expected thus far. As aresult, production efficiency of wafers of all types is improved withoutregard to whether wafers are for annealing purpose or epitaxial purpose.

In order to achieve the sixth object, the present inventors have pinneddown a combination of factors which enable miniaturization ofcrystalline imperfections and an increase in pull rate, as in the casewhere the fifth object has been achieved. By means of such acombination, the crystal pull rate is increased to a speed greater thanthat expected thus far. As a result, production efficiency of wafers forannealing purpose is improved.

Control of sizes of crystalline imperfections during the course ofmanufacture of a single crystal by use of the CZ method is delicate,because subtle elements are intertwined with each other. There is noguarantee that the common knowledge obtained without use of a coolerapplies directly to a situation in which a cooler is used. Against thisbackdrop, the present inventors have found that the effect ofminiaturizing crystalline imperfections yielded by nitrogen doping issustained even when a cooler is used. This finding has made a greatcontribution to completion of the present invention.

In a different manner, in order to solve conventional problems relatingto an increase in crystal pull rate, the present invention has provideda group of factors [i.e., an aggregation (or palette) of factors] whichpertain to an increase in crystal pull rate and miniaturization ofcrystalline imperfections and do not involve interference orneutralization. One or two or more factors are selected from the group,and an additive effect, more preferably a synergistic effect, is yieldedwith regard to an increase in crystal pull rate or miniaturization ofcrystalline imperfections.

To achieve the fifth and sixth objects, the present invention provides:

(E1) A method of pulling a silicon single crystal by use of aCzochralski (CZ) method, wherein a rate at which a silicon singlecrystal is to be pulled by use of the CZ method is increased by means ofselecting one or more factors from the group comprising adjustment of ahot zone, disposition and adjustment of a thermal shield member,adjustment of a distance between the bottom of the thermal shield memberand a melt surface, disposition and adjustment of a cooler, andapplication and adjustment of a magnetic field.

(E2) A method of pulling a silicon single crystal by use of aCzochralski (CZ) method, wherein crystal imperfections arising in asilicon single crystal to be pulled using the CZ method are reduced, bymeans of selecting one or more factors from the group comprisingadjustment of a hot zone, disposition and adjustment of a thermal shieldmember, adjustment of a distance between the bottom of the thermalshield member and a melt surface, disposition and adjustment of acooler, application and adjustment of a magnetic field, and adjustmentof doping level of nitrogen.

(E3) A method of pulling a silicon single crystal by use of aCzochralski (CZ) method, wherein speeding up of a rate at which asilicon single crystal is to be pulled according to a CZ method andminiaturization of crystal imperfections are achieved simultaneously, bymeans of disposing and adjusting a cooler, as well as selecting one ormore factors from the group comprising application and adjustment of amagnetic field, adjustment of a hot zone, disposition and adjustment ofa thermal shield member, adjustment of a distance between the bottom ofthe thermal shield member and a melt surface, disposition and adjustmentof a thermal insulation member, adjustment of a distance between thebottom of the thermal insulation member and a melt surface, andadjustment of doping level of nitrogen.

(E4) A silicon ingot for high-speed production of wafers which isproduced according to the method as defined in any one of (E1) through(E3) and miniaturizes crystalline imperfections.

(E5) A wafer for epitaxial growth or annealing purpose which is slicedoff from the silicon ingot described in (E4).

(E6) A method of optimizing a rate at which a silicon single crystal isto be pulled according to the CZ method, by means of selecting one ormore factors from the group comprising adjustment of a hot zone,disposition and adjustment of a thermal shield member, adjustment of adistance between the bottom of the thermal shield member and a meltsurface, disposition and adjustment of a cooler, application andadjustment of a magnetic field, and adjustment of doping level ofnitrogen.

(E7) A computer-readable storage medium having stored thereon two ormore data sets which are selected from the group comprising adjustmentof a hot zone, disposition and adjustment of a thermal shield member,adjustment of a distance between the bottom of the thermal shield memberand a melt surface, disposition and adjustment of a cooler, andapplication and adjustment of a magnetic field, at the time of pulling asilicon single crystal by use of a Czochralski (CZ) method.

(E8) A computer-readable storage medium having stored thereon two ormore data sets which are selected from the group comprising adjustmentof a hot zone, disposition and adjustment of a thermal shield member,adjustment of a distance between the bottom of the thermal shield memberand a melt surface, disposition and adjustment of a cooler, applicationand adjustment of a magnetic field, and adjustment of doping level ofnitrogen, at the time of pulling a silicon single crystal by use of aCzochralski (CZ) method.

(E9) A computer-readable storage medium having stored thereon two ormore data sets which are selected, along with data for disposing andadjusting a cooler, from the group comprising adjustment of a hot zone,disposition and adjustment of a thermal shield member, adjustment of adistance between the bottom of the thermal shield member and a meltsurface, disposition and adjustment of a cooler, application andadjustment of a magnetic field, and adjustment of doping level ofnitrogen, at the time of pulling a silicon single crystal by use of aCzochralski (CZ) method.

(E10) A program for increasing a rate at which a silicon single crystalis to be pulled according to the CZ method, wherein a computer-readablestorage medium has stored thereon one or more programs which areselected from the group comprising adjustment of a hot zone, dispositionand adjustment of a thermal shield member, adjustment of a distancebetween the bottom of the thermal shield member and a melt surface,adjustment of a cooler, and application and adjustment of a magneticfield.

(E11) A program for miniaturizing crystalline imperfections arising in asilicon single crystal is to be pulled according to the CZ method,wherein a computer-readable storage medium has stored thereon one ormore programs which are selected from the group comprising adjustment ofa hot zone, disposition and adjustment of a thermal shield member,adjustment of a distance between the bottom of the thermal shield memberand a melt surface, adjustment of a cooler, application and adjustmentof a magnetic field, and adjustment of doping level of nitrogen.

(E12) A program for increasing a rate at which a silicon single crystalis to be pulled according to the CZ method and for miniaturizingcrystalline imperfections, wherein a computer-readable storage mediumhas stored thereon one or more programs which are selected, along withdata for disposing and adjusting a cooler, from the group comprisingadjustment of a hot zone, disposition and adjustment of a thermal shieldmember, adjustment of a distance between the bottom of the thermalshield member and a melt surface, and adjustment of doping level ofnitrogen.

(E13) A silicon single crystal puller having stored therein the storagemedium defined in any one of (E7) through (E9) and/or the storage mediumas defined in any one of (E10) through (E12).

[Definition of Terms]

In the specification, the expression “furnace members” means materialobjects which are present within a CZ furnace. The furnace memberscomprehensively include a cooler, a thermal insulation member, a singlecrystal, a crucible, the interior wall surface of the CZ furnace, etc.

The expression “maintainability” is a broad concept including the easeof maintenance or safety.

The expression “occurrence of anomalies” implies, for example, detectionof anomalies caused by operators, power failures, failures of a vacuumpump, failures of power supply for a heater, damage to furnace members,failures of a cooling-water pump, etc.

The expression “anomalous changes in the weight of pulled singlecrystal” means that a weight change of greater than ordinary permissiblemagnitude has arisen in a single crystal being pulled. Such a change isdetected by the load imposed on a motor which pulls the single crystal.The expression “anomalous rise in the temperature of cooling water”means that a temperature change of greater than ordinary permissiblemagnitude has arisen in the cooling water circulating through thecooler. Here, a thermometer to be provided in the cooler may be embodiedin any form.

The CZ single crystal puller according to the present invention can beprovided with magnetic field application means for applying a magneticfield to a melt of material stored in a crucible. As means for applyinga magnetic field to a material melt in the crucible, there can beemployed means such as that described in, for example, Japanese PatentApplication Laid-Open No. 45889/1981. Further, as means for generating acusp magnetic field, there can be employed means such as that describedin Japanese Patent Application Laid-Open No. 217493/1983.

The silicon wafer production method and CZ single crystal pulleraccording to the present invention are not affected by the type of asingle crystal ingot to be pulled; it is thought that they can beapplied to a general CZ method. Hence, a single crystal ingot to bepulled is not limited to a silicon single crystal ingot.

The “temperature sensor” is formed from, e.g., a thermocouple. The“steam sensor” corresponds to an infrared-ray absorbency measurementsensor for detecting steam by means of changes in the absorbance ofinfrared rays. Further, the “infrared-ray absorbency measurement sensor”measures the amount of infrared rays absorbed or the ratio of absorptionof infrared rays. Further, the “infrared-ray absorbency measurementsensor” is of reflection type or transmission type.

The “thermal insulation member” is to be disposed within a furnace of aCZ single crystal ingot production system for producing a single crystalingot by use of the CZ method. The thermal insulation member is usuallydisposed so as to surround a single crystal ingot to be pulled from amelt, thus controlling the amount of heat radiated from a melt or aheater. The thermal insulation member regulates the flow of inactive gassupplied to the CZ furnace, as well as controlling the amount of heatradiated from melt or a heater. The thermal insulation member is alsocalled a “gas flow sleeve.”

The “hot zone” means an area in the CZ furnace which is directly orindirectly affected by the heating action of the heater. In some cases,the “hot zone” does not include a thermal insulation member. Theexpression “adjustment of a hot zone” means addition, modification, ordeletion of a certain member, modification of material or type of acertain member, change of layout of members, addition, change, ordeletion of moving state of a certain member, and change of energystatus of the hot zone.

The expression “distance between the bottom of the thermal insulationmember and the surface of a melt” can be measured by any means, so longas the means can appropriate measure a distance. For example, a meltlevel sensor described in Japanese Patent Application Laid-Open No.264779/2000 is preferably used. In reality, the lower end of the thermalinsulation member is changed during the course of pulling action, bymeans of thermal stress. Hence, preferably there is used a sensor, suchas that described in Japanese Patent Application Laid-Open No.264779/2000, which can accurately measure the distance between the lowerend of the thermal insulation member and the melt surface.

Throughout the specification, the expression “single crystal” is a broadconcept implying ingots, bulks, and wafers.

Throughout the specification, the expression “adjustment” is a broadconcept implying changes of any status and change of any variable, suchas adjustment of a positional relationship, a geometry, or intensity.

The expression “nitrogen doping” implies doping crystal with nitrogenduring growth, by means of introduction of nitrogen gas during thecourse of growth of a crystal or doping silicon melt with nitrides.There has been put forward a method of applying the effect ofminiaturizing defects by use of “nitrogen doping” to production of awafer for annealing purpose (as described in Japanese Patent ApplicationLaid-Open No. 98047/1998).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a preferred embodiment of a CZ singlecrystal puller according to the present invention;

FIG. 2 is a block diagram for describing the functional construction ofa hoisting and lowering apparatus of the CZ single crystal pulleraccording to the present invention;

FIG. 3 is a block diagram for describing an embodiment in which a cooleris moved in an inclined direction;

FIGS. 4A and 4B are illustrations showing embodiments of cooling stacksfor the cooler which moves in an inclined direction, wherein FIG. 4A isa side view and FIG. 4B is a top view;

FIGS. 5A through 5D are illustrations showing embodiment variations ofcooling stacks;

FIGS. 6A and 6B are block diagrams for illustrating embodiments of theCZ silicon single crystal puller equipped with a cooler, which coolerperforms rotational movement;

FIG. 7 is an illustration showing an embodiment of the cooling stack ofthe cooler which performs rotational movement;

FIGS. 8A through 8D are illustrations showing a jig to be used for ajunction between an hoisting-and-lowering block and a supply-and-exhaustpipe of a cooler, and the construction of a closure for closing holesresulting from removal of the cooler, wherein FIG. 8A is a longitudinalcross-sectional view showing the jig, FIG. 8B is a longitudinalcross-sectional view showing the closure, FIG. 8C is a top view showingthe jig, and FIG. 8D is an illustration for describing the constructionof the jig;

FIG. 9A is an illustration for describing an additional charge process;

FIG. 9B is an illustration for describing a recharge process;

FIG. 10 is a block diagram for describing the operations of the pullereffected during the additional charge process and the recharge process;

FIG. 11 is a block diagram for describing the operations of the pullereffected during the additional charge process and the recharge process,and is an illustration for describing an embodiment in which bottomheaters are included therein;

FIGS. 12A through 12D are illustrations for describing embodiments inwhich a thermal insulation member 18 is hoisted along with a cooler 19;

FIGS. 13A through 13D are illustrations for describing the operation ofthe puller effected in the embodiments in which the thermal insulationmember 18 is hoisted along with the cooler 19;

FIG. 14 is an illustration for describing the construction of asupport-plate 81;

FIG. 15 is a conceptual rendering showing an area where dislocations canbe removed by means of the Dash's neck method, which area is defined bythe relationship between the distance from the surface of a melt to thelower end of the thermal insulation member and the distance from thesurface of the melt to the lower end of the cooler;

FIG. 16 is a chart for describing the hoisting and lowering operation ofthe cooler according to the present invention, showing the position ofthe cooler (provided in an upper portion of the drawing) and a travelspeed (provided in a lower portion of the drawing) with lapse of time;

FIG. 17 is a block diagram for describing a safety device of the CZsingle crystal puller equipped with a cooler according to the presentinvention;

FIG. 18 is an illustration for describing the principle for constructinga touch sensor between members to be disposed within a furnace (furnacemembers);

FIG. 19 is an illustration showing an example connection diagram usedfor constructing a touch sensor between the furnace members;

FIGS. 20A and 20B are graphs showing the relationship between defectdensity, defect size, and concentration of nitrogen when nitrogen isadded to related-art requirements and when nitrogen is added torequirements for installing a cooler;

FIGS. 21A and 21B are graphs showing the relationship between coolingrate, defect density, and defect size when nitrogen is added torelated-art requirements and when nitrogen is added to requirements forinstalling a cooler;

FIG. 22 is a graph showing the influence of application of a magneticfield on crystal growth rate and on defect size; and

FIG. 23 shows mappings of typical LST surfaces and examples of defectdensity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a block diagram showing a preferred embodiment of a CZ singlecrystal puller according to the present invention.

[Overall Construction of the Puller]

As in the case of an ordinary CZ single crystal puller, the CZ singlecrystal puller according to the present invention comprises a chamber 11serving as a hermetic container; a crucible 13 which is provided in thechamber 11 and produces and stores silicon melt 12; and heaters 14disposed in the chamber 11 or heating the crucible 13. In addition tothese elements, other elements, such as electrodes for supplying powerto the heater 14, a crucible receiver for receiving the crucible 13, apedestal for rotating the crucible 13, heat insulators, a melt receiver,and an inner cylinder, are provided in the CZ single crystal puller, asin the case of the ordinary CZ single crystal puller. Further, the CZsingle crystal puller is provided with a thermal insulation member 18for shielding a pulled single crystal 17 from the heat radiated from thesilicon melt 12 and from the heater 14, and a cooler 19 disposed insidethe thermal insulation member 18.

Such a CZ single crystal puller pulls a single crystal 17 while thepulled single crystal 17 is rotated in the direction opposite that inwhich the crucible 13 is rotated, as in the case of the ordinary CZsingle crystal puller. The crucible 13 is moved up and down by means ofan unillustrated lifter disposed beneath the crucible 13. Unlessotherwise specified, the crucible 13 is moved vertically such that thecrucible 13 ascends in accordance with descent of a silicon melt 12 astemming from pulling of a silicon single crystal ingot.

Although not illustrated, the CZ single crystal puller according to thepresent invention is provided with an inactive gas inlet/outlet systemwhich is usually provided for a CZ single crystal puller of this type.In this system, the thermal insulation member 18 doubles as a member forregulating an inactive gas flow channel. Further, the CZ single crystalpuller is connected to a vacuum pump 20 for exhausting gas from thechamber 11. Here, if the vacuum pump 20 is provided with means fordetecting the opening of a throttle valve or the amount of electricpower supplied to the pump 20, a pressure sensor to be described latercan be omitted.

The CZ single crystal puller according to the present invention isequipped with solenoids 51 and 52 for imparting a cusp magnetic field tothe silicon melt 12. The solenoids 51 and 52 impart a cusp magneticfield to the silicon melt 12, thereby eliminating minute convectionalflows arising in the silicon melt 12. Thus, reduction of crystallineimperfections and stable pulling action can be promoted further.

As shown in FIG. 2, the CZ single crystal puller according to thepresent invention is equipped with a melt level sensor 45 for sensingthe distance between the surface 12 a of the silicon melt 12 and thebottom surface of the thermal insulation member 18, or the distancebetween the surface 12 a of the silicon melt 12 and the bottom of thecooler 19. The level of the surface 12 a—which would change verticallyin association with vertical movement of the crucible 13—can be sensedappropriately. By virtue of sensing of the level of the melt 12, thedistance between the bottom surface of the thermal insulation member 18and the surface 12 a of the silicon melt 12 or the distance between thebottom of the cooler 19 and the surface 12 a of the silicon melt 12 canbe accurately controlled so as to match a distance at which eliminationof crystalline imperfections can be achieved by the Dash's neck methodto be described later.

[Cooler]

In the CZ single crystal puller according to the present invention, thecooler 19 is disposed within the thermal insulation member 18, whereincooling water circulates through a pipe provided in the cooler 19. Asshown in FIGS. 1 and 2, the cooler 19 is formed from a multilayer pipesurrounding the pulled single crystal 17 (i.e., a cooling pipe stack),and cooling water circulates through the pipe. The cooling water issupplied by way of a supply pipe 21 a. A bellows member 23 is attachedto the area on the chamber 11 from which a supply-and-exhaust pipe 21(formed by combination of the supply pipe 21 a and an exhaust pipe 21 b)is inserted into the chamber 11, thus ensuring airtightness.

In the present embodiment, the pipe constituting the cooler 19 has aninner diameter of 17 mm or thereabouts. The speed at which cooling watercirculates through the pipe is set to 15 liters/min or less. If theinner diameter of the cooling pipe is reduced excessively, a sufficientcooling effect will not be obtained. However, if the inner diameter ofthe cooling pipe is reduced to a certain extent, the cooling effect willnot be hindered much. In this case, the amount of water circulatingthrough the cooler 19 is reduced. In the event of damage being inflictedon the cooler 19, water damage may be diminished accordingly.

The distance between the lower end 19 a of the cooler 19 and the surface12 a of the silicon melt 12 is usually set to a value of 150 mm orthereabouts. As the cooler 19 is disposed within the CZ furnace, anincrease in the temperature gradient of the body of a single crystalresults in miniaturization of crystalline imperfections. Simultaneously,the rate at which a silicon single ingot is to be pulled can beincreased, and the production efficiency of a silicon ingot can beimproved.

[Movement of the Cooler]

<A cooler hoisting-and-lowering machine (for moving the cooler linearlyin the vertical direction)>

The CZ single crystal puller according to the present invention ischaracterized in that the cooler 19 having a cooling pipe through whichcooling water circulates is moved within the CZ furnace. In the presentembodiment, the movement of the cooler 19 is embodied by “hoisting andlowering action.”

As shown in FIG. 1, the CZ silicon single crystal puller according tothe present invention is equipped with a hoisting-and-lowering machine25 for vertically moving the cooler 19 within the CZ furnace. By meansof actuation of the hoisting-and-lowering machine 25, a cooling pipestack of the cooler 19 surrounding the pulled single crystal 17 is movedvertically.

FIG. 2 is a block diagram for describing the function and configurationof the hoisting-and-lowering machine 25. In the drawing, those elementswhich are the same as the elements shown in FIG. 1 are assigned the samereference numerals, and repetition of their explanations is omitted. Forconvenience of brief explanation, members and constituent elements whichare unnecessary for explanation are omitted, and members and constituentmembers which are omitted from FIG. 1 are sometimes added forexplanation, as required.

As shown in FIG. 2, in the present embodiment, the hoisting-and-loweringmachine 25 comprises a hoisting-and-lowering block 23 a attached to anupper part of the bellows member 23 (a bridging member); ascrew-threaded shaft 25 a screwed into the hoisting-and-lowering block23 a; and a motor 26 a for rotating the screw-threaded shaft 25 a. Inthe present embodiment, the hoisting-and-lowering block 23 a and thescrew-threaded shaft 25 a are screwed together by means of a ball screw.

The hoisting-and-lowering machine 25 having the foregoing configurationhas the advantage of the ability to axially move thehoisting-and-lowering block 23 a without fail and change the travelspeed of the same freely and accurately. More specifically, there can beeffected sudden stoppage of the hoisting-and-lowering block 23 a and achange in the moving speed of reverse rotation of the same, as well asuniform motion of the hoisting-and-lowering block 23 a in the axialdirection of the screw-threaded shaft 25 a.

In the CZ single crystal puller according to the present invention, apull rate can be switched in two steps; namely, a rate of 30 mm/min. anda rate of 300 mm/min. As will be described later, this switchingfunction is utilized for ensuring the safety of the puller.

In the hoisting-and-lowering machine 25 of the foregoing embodiment,when the motor 26 a serving as a drive mechanism is stopped, the cooler19 is supported and maintained in position. Hence, energy conservationis attained.

All hoisting-and-lowering machines to be described in the embodimentmust be formed from stainless steel so as to be shielded from a magneticfield applied to a silicon melt as shown in FIG. 1. Alternatively, thehoisting-and-lowering machines must be positioned at a location wherethey are not affected by the magnetic field, or must be covered with ahousing. Thus, any measures must be taken to shield thehoisting-and-lowering machines from a magnetic field.

<Movement of the Cooler in Inclined Directions>

FIG. 3 is a block diagram for describing an embodiment in which thecooler 19 is moved in inclined directions. In the drawing, thoseelements which are the same as the elements shown in FIGS. 1 and 2 areassigned the same reference numerals, and functionally-equivalentelements are denoted by reference numerals formed by adding 1 as aprefix to the reference numeral of the corresponding elements shown inFIGS. 1 and 2.

As shown in FIG. 3, a hoisting-and-lowering machine used for moving thecooler in inclined directions is identical with that used for moving thecooler 19 shown in FIG. 1 in the vertical direction. However, the coolerdiffers from the cooler 19 in that a cooling pipe stack constituting thecooler is divided into two segments. In the CZ silicon single crystalpuller equipped with a cooler according to the present invention, whenthe cooler is moved in inclined directions, the cooling pipe stack canbe opened by virtue of such a characteristic construction of the cooler.

The construction and operation of the CZ silicon single crystal pullerequipped with a cooler 119 according to the present embodiment will bedescribed more specifically. A hoisting-and-lowering machine 125 usedfor moving, in inclined directions, the cooler 119 formed from thecooling pipe stack is essentially identical in construction with thehoisting-and-lowering machine 25 shown in FIG. 1. Eachhoisting-and-lowering machine 125 comprises a hoisting-and-loweringblock 123 a (a bridging member) attached to an upper part of a bellowsmember 123; a screw-threaded shaft 125 a screwed to thehoisting-and-lowering block 123 a; and a motor 126 a used for rotatingthe screw-threaded shaft 125 a. In the present embodiment, thehoisting-and-lowering block 123 a and the screw-threaded shaft 125 a arescrewed together by means of a ball screw, as in the case of thehoisting-and-lowering machine 25 shown in FIG. 1.

The cooler 119 according to the present invention is characterized inthat the cooler 119 formed from a cooling pipe stack is divided into twosegments; that is, cooler blocks 119 a and 119 b. As illustrated inFIGS. 4A and 4B, each of the cooler blocks 119 a and 119 b is formedinto a semi-circular form by means of coiling a cooling pipe. When thetwo cooler blocks 119 a and 119 b are joined together, a cylindricalshape is formed (see FIG. 5A). By means of such a construction, evenwhen the cooler is moved in inclined directions, the cooler can cool apredetermined position on a single crystal. Further, if cooling is notrequired, the cooler can be moved to another shunting position.

Such a cooler 119 which moves in inclined directions is not suitable forchanging a cooling position on a single crystal. However, in contrastwith the cooler which moves in a vertical direction shown in FIG. 1, thecooler 119 has the advantage of ability to accurately, easily, andquickly set or reset environmental conditions for cooling and pulling.

In the present embodiment, each of the cooler blocks 119 a and 119 bconstituting the cooler 119, which cooler moves in inclined directions,assumes a semi-circular shape (see FIG. 5A). However, the cooler blocksare not limited to the semi-circular shape. A cooler of any geometry canbe employed, so long as all the segments of a cooler constitute acylindrical or nearly-cylindrical shape when integrated together. Forinstance, there may be employed a cylindrical cooler which is dividedinto three equal segments at a central angle of 120° (see FIG. 5B) or acylindrical cooler which is divided into four equal segments at acentral angle of 90° (see FIG. 5C). As a matter of course, the centralangles of segments at which a cooler is to be divided may be nonuniform(see FIG. 5D).

<Pivotal Movement>

FIGS. 6A and 6B are block diagrams for describing an embodiment of a CZsilicon single crystal puller equipped with a cooler, which coolerperforms pivotal movement (hereinafter called a “pivotally-movablecooler”). In the drawings, those elements which are the same as theconstituent elements of the silicon single crystal puller equipped witha vertically-movable cooler shown in FIG. 1 are assigned the samereference numerals, and functionally-equivalent elements are assignedreference numerals formed by adding 2 as a prefix to the referencenumerals of corresponding elements shown in FIG. 1.

As illustrated in FIGS. 6A and 6B, a pivotally-movable cooler 219 isalso formed from a cooling pipe stack, as is the vertically-movablecooler 19. The cooler 219 cools a single crystal by means of coolingwater circulating through the cooling pipe.

This pivotally-movable cooler 219 is characterized in that the cooler219 is moved while being pivotally moved about a pivotal axis 71. In theCZ silicon single crystal puller shown in FIGS. 6A and 6B, after thecooler 219 has been lifted to a higher position by means of pivotalmovement of the cooler 219 (FIG. 6A), the bellows member 223 isextended, whereby the cooler 219 is housed in the bellows member 223(see FIG. 6B).

Expansion and contraction of the bellows member 223 are performed by ahorizontal movement machine 225. The horizontal movement machine 225 hasthe same construction as that used for moving the vertically-movablecooler 19 shown in FIG. 1 or that used for hoisting and lowering thecooler 119 which moves in inclined directions shown in FIG. 3. Thehorizontal movement machine 225 comprises a movable block 223 a attachedto the end of the bellows member 223, a screw-threaded shaft 225 ascrewed to the movable block 223 a, and a motor 226 a for rotating thescrew-threaded shaft 225 a. As in the case of the hoisting-and-loweringmachines set forth, the movable block 223 a of the horizontal movementmachine 225 moves horizontally in association with rotation of the motor226 a, thereby performing expansion or contraction of the bellows member223 and the loading/unloading of the cooler 219.

In the CZ silicon single crystal puller equipped with thepivotally-movable cooler 219, the cooler 219 assumes an imperfectcylindrical shape so that the cooler 219 can be removed from the singlecrystal 17 when the cooler 219 is lifted, as shown in FIG. 7. Basically,the cooler 219 must assume a clearance 219× that is greater than thediameter of the seed crystal 17 a. Instead of adopting a cooler of thistype, the separated cooler shown in FIGS. 5A through 5D may be employed.

[Removal of the Cooler]

The cooler 219 is removed by means of removal of the supply-and-exhaustpipe 21 from the CZ furnace after pulling of a silicon single ingot hasbeen completed.

In order to explain the cooler removal operation and relevant members, aCZ silicon single crystal puller equipped with the vertically-movablecooler 19 shown in FIG. 1 is taken as an example. So long as a puller isequipped with a cooler formed from a cooling pipe, the followingdescriptions can be applied in the same manner to another type ofpuller.

The cooler 19 is removed by means of removing the supply-and-exhaustpipe 21 (consisting of the pipes 21 a and 21 b) from the CZ furnaceafter pulling of a silicon single crystal ingot has been completed. Asshown in FIGS. 8A through 8D, the cooler 19 is fixed to thehoisting-and-lowering block 23 a by means of a fixing jig 60 provided ontop of the bellows member 23. After removal of the cooler 19, a closure70 is prepared for closing holes which would be formed in thehoisting-and-lowering block 23 a after removal of the cooler 19. Theclosure 70 is provided for the case where the cooler 19 is removed. Inorder to impart compatibility to the closure 70, the fixing jig 60 andthe closure 70 are formed so as to assume homologous shapes.

More specifically, as shown in FIGS. 8A through 8D, the fixing jig 60and the closure 70 are basically constructed such that a flange memberextending in parallel with the exterior surface of thehoisting-and-lowering block 23 a is fixed to the hoisting-and-loweringblock 23 a by means of screws. As shown in FIG. 8B, the closure 70 isconstituted of a disk-shaped flange 70 b fixed to the top of a columnarbody 70 a. While being fitted into the hoisting-and-lowering block 23 a,the closure 70 is fixed by means of a screw 70 c. An O-ring 70 d isfitted around the cylindrical body 70 a for ensuring airtightness.

As shown in FIG. 8A, the fixing jig 60 is constituted of a columnar body61 having a circumferential groove 61 a formed therein, and a pair ofsemi-circular-ring-shaped plate members 62 a and 62 b (see FIG. 8D). Theplate members 62 a and 62 b are fitted into the groove 61 a. Throughholes 61 b are formed in the columnar body 61 so as to permit insertionof the supply-and-exhaust pipe 21 (consisting of the pipes 21 a and 21b) (FIG. 8C). As in the case of the body 70 a of the closure 70, anO-ring 61 d is fitted around the columnar body 61 for ensuringairtightness.

In such a fixing jig 60, the paired semi-circular ring-shaped plates 62a and 62 b are fitted into the groove 61 a formed in the columnar body61. In this state, the semi-circular ring-shaped plates 62 a and 62 bare fixed to the columnar body 61 by means of the screws 63 a and 63 b.As a result, the fixing jig 60 assumes a columnar shape, in conjunctionwith a flange member, and can exhibit the same capability as that of theclosure 70. In the fixing jig 60 of this state, the flange sections ofthe semi-circular ring-shaped members 62 a and 62 b are fixed to thehoisting-and-lowering block 23 a by means of the screws 64 a and 64 b.

As mentioned above, the fixing jig 60 and the closure 70 (wherein thefixing jig 60 assumes a bolt-like shape when the semi-circularring-shaped members 62 a and 62 b are fitted to the columnar body 61)are fitted into the hole of the hoisting-and-lowering block 23 a as abolt-like member without threads. The fixing jig 60 and the closure 70are compatible and constitute a single set. Hence, the cooler 19 can bereadily removed from the CZ furnace. Switching between a CZ furnaceequipped with a cooler and a CZ furnace not equipped with a cooler canbe effected readily and freely. A CZ single crystal puller may be easilyused with a CZ furnace having a cooler or with an ordinary CZ furnacenot having a cooler, according to individual circumstances.

[Recharge and Additional Charge]

A quartz crucible is damaged by heating at the time of melting ofpolysilicon materials. In most cases, the quartz crucible is discardedevery pulling process. If the amount (size) of single crystal to bepulled in a single pulling process can be increased, manufacturing costscan be reduced correspondingly. Even when the same amount of singlecrystal is produced, the number of repetitions of processes, such ascooling and heating processes, can be diminished. The time required forproducing a given amount of single crystal can be diminished, and theproduction efficiency of single crystal can be improved in terms of theoverall manufacturing process. Particularly, if the amount of singlecrystal to be pulled can be increased to a useful limit of a quartzcrucible for pulling a single crystal, the effects of cost reductionscan be maximized.

Recharge and additional charge operations are measures for achieving theeffects mentioned above. As shown in FIG. 9A, according to additionalcharge operation, when polysilicon materials are melted in a quartzcrucible, the crucible is not fully charged with polysilicon materials,for reasons of bulkiness of polysilicon material. Polysilicon materialis additionally added to a melt of material, to thereby increase theamount of melt. Subsequently, a single crystal is pulled in the samemanner as in an ordinary case.

As shown in FIG. 9B, according to recharge operation, after pulling of asingle crystal has been completed to a certain extent, polysiliconmaterial is charged to a crucible, and pulling of the single crystal isresumed.

The recharge and additional charge operations enable an increase in theamount (size) of single crystal which can be pulled in a single pullingprocess, thus diminishing manufacturing costs. Since these operations donot involve significant heating or cooling of a crucible, shortening ofcrucible life is prevented, thus extending a heating time. Even in thisrespect, the length of a single crystal to be pulled in a singleoperation can be increased by the amount corresponding to an increase ina heating time. If a cooler is used for a recharge or additional chargeoperation, the overall production efficiency can be increased by virtueof an increase in the amount of single crystal to be pulled per unittime as a result of an increase in the pull rate induced by use of thecooler.

In order to cause the cooler 19 and the thermal insulation member 18 tosufficiently exhibit their capabilities, they are disposed at positionsclosest to the surface of a melt. However, at the time of recharge oradditional charge operation, the surface of ascending melt may touchthem, or they may be splashed with a melt. For these reasons, arrangingthe cooler 19 and the thermal insulation member 18 near a melt surfaceis not preferable.

The same problems arise when material is charged to a crucible by meansof an ordinary charging operation. Hence, realization of a fully-chargedstate for increasing production efficiency inevitably involves anincrease in the amount of polysilicon material to be piled up. In such acase, polysilicon material piled in an upper position falls during thecourse of melting operation, whereupon the cooler 19 and the thermalinsulation member 18 may be splashed with a melt of material.

In order to solve such problems, the CZ silicon single crystal pullerequipped with a cooler according to the present invention moves thecooler and the thermal insulation member to their higher, retractedpositions at the time of charging material into a crucible, meltingmaterial, and recharge or additional charge operation (see FIG. 10). Inthis case, the previously-described hoisting-and-lowering mechanism maybe used as a mechanism for moving a cooler. Further, in terms of workingefficiency, the cooler and the thermal insulation member are preferablymoved to their higher, retracted positions at high speed (300 mm/min.).

If the foregoing technique according to the present invention isemployed, in a case where heating power is increased by means ofadditionally providing, for example, a bottom heater 16 to the CZfurnace as shown in FIG. 11, the cooler 19 and the thermal insulationmember 18 are moved to their higher, retracted positions, thusprotecting them from splash of a melt. As a result, increased heatingpower can be effectively utilized for melting material.

[Movement of the Thermal Insulation Member Following the Cooler]

FIGS. 12A through 12D are longitudinal cross-sectional views of the CZfurnace for describing the construction and function of the thermalinsulation member and those of the cooler according to the presentinvention.

As shown in FIG. 12A, the present invention is characterized in that atab member 81 a is attached to the side of the cooler 19 and that anengagement member 18 a to be engaged with the tab member 81 a isprovided on the interior wall surface of the thermal insulation member18. The thermal insulation member 18 is simply placed on a table member83 within the CZ furnace without use of screws or bonding. Hence, solong as the thermal insulation member 18 is lifted, the member 18 can beeasily detached from the table member 83.

As shown in FIGS. 12B and 12C, in the CZ single crystal puller equippedwith a cooler according to the present invention, when the cooler 19 islocated in an ordinary position, the tab member 81 a is not engaged withthe engagement member 18 a, and the cooler 19 and the thermal insulationmember 18 remain in their ordinary states. As illustrated, the tabmember 81 a and the engagement member 18 a are arranged in a positionalrelationship in which they are to engage. Hence, when the cooler 19 ishoisted, the tab member 81 a is engaged with the engagement member 18 a.Accordingly, the thermal insulation member 18 is also lifted andseparated from the table member 83 along with the cooler 19.

As shown in FIG. 12C, the tab member 81 a is provided not over theentire circumference of the cooler 19, but in several positions alongthe circumference of the cooler 19. Similarly, the engagement member 18a is provided on several positions along the interior circumference ofthe thermal insulation member 18. In the example shown in FIG. 12C, twotab members 81 a and two corresponding engagement members 18 a areprovided. Alternatively, three tab members 81 a and three correspondingengagement members 18 a may be provided on the cooler 19 and the thermalinsulation member 18, respectively, as illustrated in FIG. 12D. Furtheralternatively, they may be provided in a number greater than three inconsideration of the overall function of a CZ single crystal puller.

FIGS. 13A through 13D are illustrations for describing the operation ofthe cooler 19 and that of the thermal insulation member 18 according tothe present invention. In these drawings, those elements which areidentical with the constituent elements shown in FIG. 11 and FIGS. 12Athrough 12D are assigned the same reference numerals, and repetition oftheir explanations is omitted.

As shown in FIG. 13A, the cooler 19 is placed at a home position; thatis, at a lowest-level position. As shown in FIG. 13B, the cooler 19 ishoisted. When the tab member 81 a is engaged with the engagement member18 a, as shown in FIG. 13C, the thermal insulation member 18 a is lifted(FIG. 13D). Conversely, as shown in FIG. 13B, the cooler 19 can befreely moved in the vertical direction independently of the thermalinsulation member 18 until the tab member 81 a is engaged with theengagement member 18 a.

In a case where the tab member 81 a is bonded to the side surface of themetal cooler 19, difficulty is usually encountered in ensuring thestrength sufficient for establishing engagement with and lifting thethermal insulation member 18. Accordingly, in a preferred embodiment,the support plate 81 such as that shown in FIG. 14 is formed. Thesupport plate 81 is then inserted into a helical indent formed in thecoiled cooling pipe of the cooler 19 such that the tab members 81 aproject from the side wall of the cooler 19. More specifically, thesupport plate 81 is constituted of an annular portion 81 b to beinserted into the helical indent of the cooler 19, and the tab members81 a projecting outward from the annular portion 81 b. When the supportplate 81 is fitted into the cooler 19, the tab members 81 a project fromthe side wall of the cooler 19, as illustrated in any of FIGS. 13Athrough 13D. The tab members 81 a project from the side wall of thecooler 19, and the tab members 81 a can offer strength sufficient forlifting the thermal insulation member 18. The support plate 81 can beformed from heat-resisting material, such as carbon material.

In the CZ single crystal puller equipped with a cooler according to thepresent invention, the cooler 19 is moved to a higher position away fromthe surface of a melt at the time of initial melting of material or atthe time of melting of material with a recharge or additional chargeoperation, in order to shorten a melt time. At this time, in the presentembodiment, the thermal shield member 18 is also moved to a higherposition along with the cooler 19. Hence, the thermal shield member 18casts a shadow on the cooler 19, thus shielding the cooler 19 from themelt surface. As a result, the efficiency of heating for meltingmaterial is increased. When material is initially melted, or whenmaterial is recharged or additionally charged, the proportion of outputof, particularly, the bottom heater 16 is preferably increased at thetime of melting material, thus shortening a melt time.

Vertical movement of the cooler 19 is performed at high speed when thecooler 19 is moved to a higher position for the reason set forth, or toa retracted position for safety. In contrast, when the cooler 19 islowered to a lower position during growth of crystal, the cooler 19 islowered gradually in order to avoid occurrence of sudden changes inthermal environment.

Although the additional charge and recharge operations have beendescribed herein by means of taking, as an example, the CZ singlecrystal puller equipped with a vertically-movable cooler, one of theobjectives of the present invention can be achieved so long as thecooler has been moved to a position away from a melt or a crucible whenadditional charge or recharge operation is performed. Hence, it isevident that the present invention can be applied to various CZ singlecrystal pullers, such as a CZ single crystal puller equipped with acooler which moves in inclined directions and a CZ single crystal pullerequipped with a pivotal cooler.

[Dash's Neck Method and Cooler]

Through their studies, the present inventors have found that, when acooler is present close to a seed crystal during the course of drawingof a seed crystal according to the Dash's neck method, dislocations dueto thermal shock fail to be eliminated from the seed crystal, thushindering manufacture of a single crystal (see Table 1). TABLE 1REQUIREMENTS FOR ENABLING ELIMINATION OF DISLOCATIONS (TEST DATA) S:DISTANCE BETWEEN MELT 20 30  40 20 AND LOWER END OF THERMAL INSULATIONMEMBER (mm) C: DISTANCE BETWEEN MELT 75 125 85 115 — AND LOWER END OFCOOLER (mm) PERCENT ELIMINATION OF 0/3 0/1 15/15 1/1 15/15 DISLOCATIONS(DENOMINATOR IS THE NUMBER OF TESTS)

As shown in Table 1, when the distance between the thermal insulationmember 18 and the melt surface was 20 mm, dislocations could not beremoved from a seed crystal, regardless of whether the distance betweenthe cooler 19 and the melt surface was small (75 mm) or large (125 mm)(as shown in Table 1, the percent elimination of dislocations is 0% ineither case). In contrast, when the distance between the thermalinsulation member 18 and the melt surface was 30 or 40 mm, a percentelimination of dislocations of 100% was achieved, regardless of whetherthe distance between the cooler 19 and the melt surface was small (85mm) or large (115 mm) (as shown in Table 1, dislocations were eliminatedfrom all 15 crystals when the distance between the thermal insulationmember 18 and the melt surface was 30 mm). In contrast, when no coolerwas disposed in the CZ furnace (the rightmost column in Table 1), thepercent elimination of dislocations of 100% was attained even when thedistance between the thermal insulation member 18 and the melt surfacewas 20 mm.

As mentioned above, when no cooler is present in the CZ furnace,dislocations can be eliminated from a seed crystal even when the lowerend of the thermal insulation member is located in the vicinity of themelt surface. However, it is understood that, when a cooler is presentin the CZ furnace, elimination of dislocations becomes impossible if thelower end of the thermal insulation member is spaced a certain distanceaway from the melt surface (i.e., a distance of at least 30 mm orthereabouts from the melt surface).

On the basis of such data, there is assumed an area in which eliminationof dislocations becomes feasible (hereinafter the area will be called a“dislocation-elimination range”), as shown in FIG. 15. Specific numeralsrelated to a boundary region of the dislocation-eliminating range shownin FIG. 15 are determined by means of the size and status of a CZfurnace and the geometries of members used within the furnace. Forinstance, in the present embodiment, point P in the drawing is 30 mm.

When the cooler 19 and the thermal insulation member 18 are locatedclose to the melt surface, dislocations are not eliminated. In otherwords, elimination of dislocations from a seed crystal by use of theDash's neck method involves separation of the thermal insulation member18 and the cooler 19 from the melt surface.

Accordingly, in the present invention, the cooler 19 and the thermalinsulation member 18 are controlled so as to be separated from the meltsurface during the course of elimination of dislocations by use of theDash's neck method. The distance over which the cooler 19 and thethermal insulation member 18 are to be separated from the melt surfaceis determined after boundary conditions of the dislocation-eliminativerange shown in FIG. 15 have been specifically determined in accordancewith the size and status of a CZ furnace and geometries of members to beused in the CZ furnace. The cooler 19 and the thermal insulation member18 are moved so as to enter the dislocation-elimination range.

After dislocations have been sufficiently eliminated from a seed crystalby use of the Dash's neck method, the cooler 19 and the thermalinsulation member 18 are lowered, and a single crystal is pulled whilebeing cooled. During the course of this operation, the cooler 19 and thethermal insulation member 18 are basically and preferably moved at ahigh speed (300 mm/min.), in consideration of working efficiency.

The operation of the cooler effected for eliminating dislocations from acrystal by use of the Dash's neck method has been described, by means oftaking a CZ single crystal puller equipped with the vertically-movablecooler according to the present invention. One objective of the presentinvention is to separate a cooler and a thermal insulation member at apredetermined distance from a melt surface during the course ofelimination of dislocations by use of the Dash's neck method. Hence, itis evident that the present invention can be applied to various CZsingle crystal pullers, such as a CZ single crystal puller equipped witha cooler which moves in inclined directions and a CZ single crystalpuller equipped with a pivotal cooler.

[Relationship Between the Travel Speed and Position of the Cooler forAll Single-Crystal Pulling Processes]

FIG. 16 is a graph for describing the operation of the CZ single crystalpuller equipped with a cooler according to the present invention. Alower graph shows a travel speed of a cooler, and an upper graph showsthe position of the cooler.

In a process for performing an additional charge operation and a neckingoperation (i.e., processes A and B), the cooler 19 is situatedstationarily at a higher position away from the melt surface. After thenecking operation has been completed, the cooler 19 is lowered to apredetermined position and comes to standstill (process C). At thistime, the cooler 19 is moved at high speed for speeding up the work. Ifchucking of a seed crystal is again required, the cooler 19 is againlifted to a higher position, and the necking operation is againperformed in this state.

Subsequently, a single crystal is pulled while the cooler has beenlowered to a predetermined position (process D). Since the singlecrystal is pulled while being cooled, a pull rate can be increased.Here, after pulling of a single crystal has been completed, the cooler19 is lifted at high speed (process E). In order to effect remelting ofmaterial, the cooler 19 is stopped at the higher position (process F).After completion of a remelting operation, the cooler 19 is lowered athigh speed (process G), and a single crystal is pulled again (processH). In a tail process (process I), which is the final process of thesingle crystal pulling operation, the cooler 19 is lifted for reducingpower consumption. In order to ensure sufficient melt, the cooler 19 islifted at a slightly-lagged timing.

Next, at the time of a recharge operation (process J) being performed,the cooler 19 is lifted to a higher position for ensuring ease ofrecharge operation and preventing damage to furnace members, which wouldotherwise be caused by splashing of melt. After completion of therecharging operation, the cooler 19 is gain lowered at high speed(process K), and a single crystal is pulled (process L). In the event ofoccurrence of collision or accident, the cooler 19 is lifted immediatelyduring the single crystal pulling process (i.e., process L), thusseparating the cooler 19 away from the surface of a silicon melt. In thetail process (process M) subsequent to pulling of a single crystal,there is effected processing which is the same as that effected in thepreviously-described tail process (process I). Subsequently, the cooler19 is lowered to a position within the crucible (process N), and thecrucible is cooled (process 0).

<Operation for Ensuring Safety and Avoiding Hazards>

In principle, as an operation for ensuring safety and avoiding hazards,the CZ single crystal puller according to the present invention movesthe cooler away (to a retracted position) from a location whereanomalies have arisen, a melt surface, or a single crystal being pulled.For example, if the expression “anomalies” signifies collision betweenthe cooler 19 and another furnace member or a near miss arising betweenthe cooler 19 and another furnace member, there is mentioned a method oftemporarily moving the cooler 19 in reverse by a distance of about 5 mm.If the expression “anomalies” signifies collision between furnacemembers other than the cooler 19, or erroneous operations of the CZsingle crystal puller, the cooler 19 is moved away from the singlecrystal 17 and the silicon melt 12, thereby avoiding hazards. Hence, themaintainability of the CZ single crystal puller is improved.

In this case, when the cooler 19 is moved away from hazardous areastypified by the single crystal 17 and the silicon melt 12, the cooler 19is moved while a travel speed is switched to a higher speed (e.g., 30mm/min. to 300 mm/min.), thus enabling immediate avoidance of hazards.

A mechanism and device for sensing anomalies can be embodied by means ofdetecting the temperature of cooling water circulating through thecooler, monitoring the internal temperature distribution of the CZfurnace, sensing relative positions of furnace members, sensing of aload imposed on a cooler or that imposed on a single crystal pullingmotor, sensing variations in an abnormal weight, and sensing the amountof travel of a cooler through use of an encoder provided in a movablecooler. In the specification, the function and construction of a sensingmechanism and device, which device is employed in the CZ single crystalpuller and ensures safety by means of sensing particularly moisture,will be described by reference to FIG. 1.

As shown in FIG. 1, the CZ single crystal puller according to thepresent embodiment comprises a pressure sensor 31 for tracing variationsin the internal pressure of the chamber 11; a temperature sensor 33 forsensing variations in the temperature of a gas which is stored in thechamber 11 and is to be evacuated by the vacuum pump 20; and aninfrared-ray sensor 34 for sensing infrared rays absorbed by the gaswhich is stored in the chamber 11 and is to be evacuated by the vacuumpump 20. In the event of water leakage arising in the pipe of the cooler19, the leaked water is changed into steam by the heat in the furnace,and the steam in turn causes variations in temperature or pressure ofthe furnace. By means of sensing a change in temperature or pressure inthe furnace, water leakage can be sensed accurately. Since steam absorbsinfrared rays, the infrared-ray sensor 34 is provided for enhancing theaccuracy of detection of water leakage by means of determiningabsorption of infrared rays.

If any one of the above-described sensors is disposed in the furnace,water leakage can be sensed sufficiently. However, in order to make allpossible preparations for sensing water leakage, a plurality of sensorsmay be disposed in combination. For the same reason, a plurality ofsensors of the same type may also be disposed.

Unless a comparatively large amount of steam is present, the temperaturesensor 33 will fail to sense variations in temperature distinguishablyfrom changes in another condition. For this reason, in order toaccurately sense variations in temperature caused by steam, thetemperature sensor 33 must be disposed in a position at which steamconcentrates. Basically, the temperature sensor 33 is preferablydisposed in an exhaust channel (i.e., a pipe connected to the vacuumpump 20). Since the infrared-ray sensor 34 can immediately sense a traceamount of steam, the sensor can be attached not only in the exhaustchannel but anywhere, such as an interior wall surface of the chamber11.

The sensors are connected to the controller 35. In the presentembodiment, the pressure sensor 31 is connected directly to thecontroller 35. Further, the temperature sensor 33 is connected to thecontroller 35 byway of a corresponding processor 33 a, and theinfrared-ray sensor 34 is connected to the controller 35 by way of acorresponding processor 34 a.

For example, if a rise in the internal pressure of the chamber 11stemming from generation of steam has been sensed by the presser sensor31, if the temperature sensor 33 has sensed an increase in thetemperature of an exhaust gas resulting from generation of steam, if theinfrared-ray sensor 34 has sensed abnormal absorption of infrared raysin the absorption range of steam, or if all these situations haveoccurred simultaneously, the controller 35 is activated, to therebyilluminate an indicator 36. Further, the controller 35 closes a solenoidvalve 37 for regulating inflow of cooling water, thus stopping inflow ofcooling water. Simultaneously, another solenoid valve 39 which usuallyremains closed is opened, thereby opening the end of the exhaust pipe 21b to the atmosphere. In the event of occurrence of water leakage, leakedwater is changed to steam, thus resulting in an increase in pressure. Inthis case, cooling water circulating through the cooler 19 is dischargedto the outside by way of the solenoid valve 39, thereby diminishing theamount of water dropping into silicon melt.

The pipe to be released to the atmosphere is also connected to thesupply tube 21 a, and hence cooling water which is about to be suppliedto the cooler 19 can also be discharged. By means of such a tube, in theevent of occurrence of water leakage, the cooling water still remainingin the cooler 19 can be discharged in as great an amount as possible,thus lessening damage which would be inflicted on the CZ single crystalfurnace. Even in such a case, closedown of the CZ single crystal furnacecan be avoided. In order to make preparations against emergency, thechamber 11 of the CZ single crystal puller according to the presentembodiment is provided with a safety valve 40. Further, check valves 41,42, and 43 are attached to a cooling-water outlet pipe or a non-pressurepipe. Thus, all possible preparations against emergency are taken.

In the specification, “anomalies” arising in the CZ single crystalpuller may imply, for example, detection of anomalies by operators,power failures, failures of a vacuum pump, failures of power supply fora heater, damage to furnace members, failures of a cooling-water pump,etc. If such “anomalies” arise, at least the motor 26 a of thehoisting-and-lowering machine 25 is stopped. In some instances, themotor 26 a i's quickly rotated in reverse, thereby moving the cooler 19in a reverse direction, thereby preventing occurrence of a more seriousproblem which would otherwise arise. Moreover, in order to avoidoccurrence of a serious problem, in the event of occurrence of“anomalies,” a cooler is moved at high speed (300 mm/min.) away fromfurnace members (i.e., the surface of a silicon melt and a singlecrystal), which would be dangerous were the cooler to approach them.

The CZ single crystal puller equipped with a cooler according to thepresent invention can prevent occurrence of problems, which wouldotherwise be caused at the time of a recharge operation or an additionalcharge operation, at the time of elimination of dislocations using theDash's neck method, or by a cooler disposed within a CZ furnace forcooling a single crystal. The puller can provide solely a merit ofspeeding up of a crystal pull rate induced by a cooler. Hence, the CZsingle crystal puller equipped with a cooler according to the presentinvention can reliably yield such an advantage of speeding up a crystalpull rate to 1.5 times that of the related-art CZ single crystal puller,without involvement of a demerit, which would otherwise be caused by acooler.

More specifically, the CZ single crystal puller equipped with a cooleraccording to the present invention can lessen a problem of an increasein the energy consumed by a CZ single crystal puller equipped with acooler. In the CZ single crystal puller equipped with a cooler such asthat described herein, the crystal pull rate can be increased to 1.5times the rate of a related-art CZ single crystal puller, by means ofinterposing a cooler between a crystal and a thermal insulation memberfor shielding the crystal from the heat originating from the materialmelt. However, such an increase in pull rate involves a problem of anincrease in energy consumption. In contrast, in the CZ single crystalpuller equipped with a cooler according to the present invention, acooler (along with a thermal insulation member in some cases) is movedto a higher position at the time of a first melting operation, meltingwith additional charge, or melting with recharge. Hence, the output ofthe heater is diminished correspondingly, thereby suppressing anincrease in energy consumption.

Further, the CZ single crystal puller equipped with a cooler accordingto the present invention solves problems which are posed by thedurability of a quartz crucible and arise at the time of additionalcharge or recharge operation. When an additional charge or rechargeoperation is performed, the quartz crucible remains heated over a longperiod of time, which in turn involves problems of deterioration of thequartz crucible or durability. If a recharge operation has beenperformed, yield of crystal is deteriorated by an increase in the rateof collapse of a crystal (polycrystallization) after recharge operation.If an additional charge operation has been performed, yield of crystalis deteriorated by an increase in the rate of collapse of a crystal(polycrystallization) during the course of growth of the latter half ofthe crystal. In contrast, the CZ single crystal puller equipped with acooler according to the present invention enables reliable increase ofthe crystal pull rate to 1.5 times or more that of the related-art CZsingle crystal puller without involvement of a demerit, which wouldotherwise be posed by installation of a cooler, thus shortening the timefor heating the quartz crucible. Therefore, the rate of elimination ofdislocations can be increased for both a crystal produced throughadditional charge and a crystal produced through recharge. In terms ofdurability, until now use of an expensive synthetic quartz has beenrequired, for avoiding an increase in the rate of polycrystallization.However, adoption of the present invention enables use of a naturalquartz crucible.

Further, although the CZ single crystal puller according to the presentinvention is provided with a cooler, elimination of dislocations can beeffected without fail, by use of the Dash's neck method. Hence,production efficiency is increased, thus contributing to reduction inproduction costs.

Even when furnace members are deformed as a result of long-term use,substantially identical requirements can be maintained by means offinely adjusting the distance between a melt surface and a cooler andthe distance between a thermal insulation member and a cooler, thusenabling continuous production of crystal of stable quality.

[Safety Device]

As mentioned above, the present invention enables movement of the coolerdisposed within a CZ furnace of the CZ single crystal puller. In theevent of anomalies arising in the puller, the cooler is moved away fromthe area where the anomalies have arisen, thus enhancing safety of thepuller.

<Operations for Ensuring Safety and Avoiding Hazards>

A basic safety protocol employed by the CZ single crystal pulleraccording to the present invention for ensuring safety and avoidinghazards is to move a cooler away from an area where anomalies havearisen, a melt surface, or a pulled single crystal. More specifically,when “anomalies” correspond to collision or near miss arising betweenanother furnace member and the cooler 19 in the course of verticalmovement, there may be employed a procedure for temporarily moving thecooler 19 in reverse by 5 mm or thereabouts. If “anomalies” correspondto collision between furnace members other than the cooler 19 or faultyoperations of the puller, the cooler 19 is moved away from the singlecrystal 17 or the silicon melt 12, thus avoiding hazards and enhancingthe safety of the CZ single crystal puller.

In this case, when the cooler 19 is moved away from perilous areastypified by the pulled single crystal 17 and the silicon melt 12, thecooler 19 is moved by means of changing travel speed to a higher speed(e.g., 30 mm/min. to 300 mm/min.), thus enabling immediate avoidance ofhazard.

Specific Embodiments of a Safety Device

A safety device provided in the CZ single crystal puller equipped with acooler according to the present invention will now be described.

FIG. 17 is a block diagram for describing a safety device of the CZsingle crystal puller equipped with a cooler according to the presentinvention. In the drawing, those elements which are the same as theconstituent elements shown in FIGS. 1 and 2 are assigned the samereference numerals, and repetition of their explanations is omitted. Forthe convenience of explanation, explanation is given of the safetydevice in the present embodiment by reference to the CZ single crystalpuller having the vertically-movable cooler 19. However, it is obviousthat the safety device can be applied to the cooler 119 which moves ininclined directions and to the pivotal cooler 219, without involvementof changes in the basic principle.

<Detection of Temperature>

The CZ single crystal puller equipped with a cooler according to thepresent invention is provided with a radiation thermometer/CCD camera 72for two-dimensionally observing the inside of a CZ furnace by way of awindow formed in the chamber 11. The radiation thermometer/CCD camera 72acts as a thermograph for sensing the internal temperature distributionof the CZ furnace, thereby sensing any anomalous rise in the surfacetemperature of the cooler 19.

In the present embodiment, a temperature sensor 73 formed from athermocouple is provided on the interior of the cooler 19. Thetemperature sensor 73 can also sense an anomalous rise in the surfacetemperature of the cooler 19. When the temperature sensor 73 is attachedto the exterior of the cooler 19, the sensor can sense excessive heatingof the heater 14.

As mentioned above, the CZ single crystal puller equipped with a cooleraccording to the present invention is provided with the radiationthermometer/CCD camera 72 or the temperature sensor 73, and either ofthese enables detection of an anomalous rise in the surface temperatureof the cooler 19. In a case where an anomalous rise in the surfacetemperature of the cooler 19 has been detected, the cooler 19 is movedaway at high speed (e.g., 300 mm/min.) from an area which is ascribableto the temperature rise (e.g., the pulled single crystal 17), thusavoiding occurrence of a serious accident.

According to one selective embodiment of the present invention, the CZsingle crystal puller equipped with a cooler is provided with athermometer 74 for detecting the temperature of the cooling water thathas passed through the cooler 19. If the thermometer 74 has detected ananomalous rise in cooling water temperature, the cooler 19 is moved awayfrom the location which is ascribable to the anomalous rise in thetemperature of cooling water (e.g., the pulled single crystal 17 or thesurface of silicon melt 12). In this case, the movement of thevertically-movable cooler 19 is limited to the vertical direction.Hence, movement of the cooler 19 away from the surface of silicon meltis predominant. However, in the case of the cooler 119 which moves ininclined directions and in the case of the pivotally-movable cooler 219,if the cooler is separable, the cooler can be moved away from thesurface of the silicon melt 12 and from the pulled single crystal 17simultaneously.

<Detection of Relative Position>

The CZ single crystal puller equipped with a cooler according to thepresent invention is provided with a melt level sensor 75 for sensingthe level of a silicon melt. The melt level sensor 75 can measure, inaddition to the level of the silicon melt, the distance between thebottom surface of the cooler 19 and the upper surface of the thermalinsulation member 18, and the heights of ordinary furnace members.Accordingly, the melt level sensor 75 can detect near miss or collisionbetween furnace members, which would otherwise be caused in associationwith vertical movement (hoisting and lowering action) of the cooler 19.

In a case of employment of a two-dimensional melt level sensor describedin, for example, Japanese Patent Application Laid-Open No. 264779/2000,a vertical distance and a horizontal distance can be sensed. As aresult, the melt level sensor can detect near miss or collision arisingbetween the thermal insulation member 18 and the single crystal 17 andnear miss or collision arising between the cooler 19 and the singlecrystal 17, as well as near miss or collision arising between the bottomof the cooler 19 and the thermal insulation member 18. A horizontaldistance can be detected by means of the radiation thermometer/CCDcamera 72.

As mentioned above, the CZ single crystal puller equipped with a cooleraccording to the present invention is provided with the melt levelsensor 75 (particularly, the two-dimensional melt level sensor) or theradiation thermometer/CCD camera 72. Either of these enables detectionof near miss or collision arising between the cooler 19 and the singlecrystal 17 or near miss or collision arising between furnace members. Ifnear miss or collision has been detected during the hoisting or loweringoperation, the motor 26 a of the hoisting-and-lowering machine 25immediately rotates in reverse, thus moving the cooler 19 in the reversedirection and avoiding occurrence of a serious accident. In some cases,as in the case of detection of temperature, the cooler 19 is moved athigh speed (300 mm/min.) away from the surface of the silicon melt 12and the pulled single crystal 17, thereby avoiding occurrence of aserious accident.

<Encoder>

The CZ single crystal puller equipped with a cooler according to thepresent invention is provided with an encoder 26 b integrated with amotor 26 a (see FIG. 2). The distance over which the cooler 19 ishoisted or lowered is traced by means of the encoder 26 b.

On the basis of a value computed from the information (the distance overwhich the cooler 19 is hoisted or lowered) supplied from the encoder 26b, if there is detected near miss or collision arising between thecooler 19 in vertical motion and the pulled single crystal 17(particularly in the case of the cooler 119 which moves in inclineddirections or the pivotally-movable cooler 219), or near miss orcollision arising between the cooler 19 and a material melt or anotherfurnace member (in the case of any of the vertically-movable cooler 19,the cooler 119 which moves in inclined directions, and thepivotally-movable cooler 219), reverse rotation of the motor 26 a orswitching of travel speed of the cooler (speeding up of the cooler) iseffected, thereby moving the cooler away from a perilous area, such asthe location at which near miss or collision has been detected, thesurface of silicon melt, or the pulled single crystal 17.

<Limiter Member>

The CZ single crystal puller equipped with a cooler according to thepresent invention is provided with a limiter switch (LS) 27 disposed ata position below the hoisting-and-lowering block 23 a (FIG. 2). In theevent that the hoisting-and-lowering block 23 a has come into contactwith the LS 27, the motor 26 a is stopped immediately, thereby stoppinglowering action of the cooler 19. In some cases, the motor 26 a isactively rotated in reverse, thereby returning the cooler 19 to a higherposition.

Here, the limiter switch (LS) 27 is in principle for setting a lowerlimit below which the cooler 19 is not lowered further (i.e., a limitermember). The size of the limiter switch LS 27 is set in accordance withthe lower limit. In the present embodiment, a limiter switch whicheffects electrical control is employed as the limiter member. However,the limiter member may be embodied by a physical substance or a solidmember such as a mere metal block, so long as the substance can limitlower movement of the hoisting-and-lowering block 23 a below apredetermined location.

The CZ single crystal puller equipped with a cooler according to thepresent invention is provided with such a limiter member, whereby atleast excessive lowering of the cooler 19 can be prevented by use ofphysical limitations. If the limiter member is constituted of a limiterswitch, recovery of the cooler 19 from an excessively-lowered state canbe effected immediately.

<Touch Sensor>

In order to accurately detect contact between furnace members(particularly contact between the cooler moving within the furnace andanother furnace member), the CZ single crystal puller equipped with acooler according to the present invention is configured so as to apply aconstant voltage to members whose mutual contact is desired to bedetected while the members are insulated, and to trace variations in thevoltage. In short, a touch sensor is constructed over members whosemutual contact is to be detected. FIG. 18 shows the principle of thetouch sensor, and FIG. 19 shows one example of a required schematicdiagram. Although the present embodiment illustrates construction of atouch sensor of voltage measurement type, the previously-described touchsensor of current measurement type may be constructed. In the drawings,those elements which are the same as the constituent elements shown inFIGS. 1 and 2 are assigned the same reference numerals, and repetitionof their explanations is omitted.

In order to detect contact between the cooler 19 and another furnacemember, the cooler 19 is insulated from other furnace members. As shownin FIG. 18, insulation of the cooler 19 is implemented by means ofattaching the supply-and-exhaust pipe 21 to the hoisting-and-loweringblock 23 a with an insulation member 80 a sandwiched therebetween.Further, as shown in FIG. 18, in order to detect contact between thethermal insulation member 18 and another furnace member, an insulationmember 80 b is preferably attached to the base end of the thermalinsulation member 18, and a wire is preferably connected to the thermalinsulation member 18. Similarly, in order to detect contact of thecrucible 13 and the silicon melt 12 with another furnace member, aninsulation member 80 c is preferably attached to a lower portion of thepedestal or a lower portion of a crucible shaft, and a wire ispreferably connected to the crucible 13. In order to detect contact ofthe pulled single crystal 17 and the wire 15 for pulling the pulledsingle crystal 17 with another furnace member, an insulation member 80 dis preferably interposed between a take-up machine 16 for taking up thewire 15 and the top of the chamber 11. A wire is connected to thetake-up machine 16.

FIG. 19 is an example connection diagram used for constituting a touchsensor across furnace members. As shown in FIG. 19, in order toconstitute a touch sensor between the cooler 19 and another furnacemember and to detect contact therebetween, the cooler 19 is insulatedfrom another furnace member through use of the insulation member 80 ashown in FIG. 18. A constant voltage is applied between the cooler 19and the furnace member. A constant-voltage power supply 81 applies aconstant voltage. Preferably, one terminal of the constant-voltage powersupply 81 is connected to the supply-and-exhaust pipe 21 of the cooler19, and the other terminal of the constant-voltage power supply 81 isconnected to the exterior wall of the chamber 11.

In the touch sensor circuit, a voltage detector 82 is connected inparallel to the constant-voltage power supply 81. In the presentembodiment, the touch sensor circuit is further provided with a relayswitch 83 which is activated only during the course of automaticoperation. When the relay switch 83 is activated when automaticoperation is performed, a touch sensor is formed at least between thecooler 19 and the chamber 11.

In this state, when the cooler 19 comes into contact with anotherfurnace member, the voltage detector 82 detects a drop in voltage.Hence, so long as a voltage drop is traced by the voltage detector 82,near miss or collision between the cooler 19 and another furnace memberor near miss or collision between furnace members can be detected. Whensuch near miss or collision is detected, the motor 26 a of thehoisting-and-lowering machine 25 is immediately rotated in reverse,thereby retracting the cooler 19, thus preventing occurrence of aserious accident. In some cases, as in the case of the embodiment inwhich temperature detection is effected, the cooler 19 is moved awayfrom the surface of a silicon melt or the pulled single crystal 17 athigh speed (300 mm/min.), thus avoiding occurrence of a seriousaccident.

In a case where the cooler 19 is insulated from other furnace membersthrough use of the insulation member 80 a and where the insulationmembers 80 b through 80 d are not provided in the furnace, only contactof the cooler 19 with another furnace member can be detected. However,the type of the furnace member that has come into contact with thecooler 19 cannot be determined. For this reason, the insulation members80 b, 80 c, and 80 d are provided, and corresponding constant-voltagepower supplies and voltage detectors are connected to the insulationmembers 80 b through 80 d. As is obvious from the principle of the touchsensor according to the present invention, such a construction enablesdetection of contact between the thermal insulation member 18 andanother furnace member, contact of the crucible 13 and the silicon melt12 with another furnace member, and contact between the pulled singlecrystal 17 and the wire 15, in this sequence. In a case where all theinsulation members 80 a through 80 d shown in FIG. 18 are provided onthe corresponding furnace members, when the terminal of theconstant-voltage power supply 81 is connected to the chamber 11 andcontact is detected, the furnace member that has caused contact can bedetected accurately, as has been described previously.

In a case where a touch sensor is constructed between furnace members inthe CZ single crystal puller, the greater the number of insulationmembers 80 to be attached to the furnace and the greater the number ofvariations of the insulation members, the higher the accuracy of thetouch sensor is increased. The number of insulation members 80 andvariations thereof are determined in comprehensive consideration of theimportance and level of emergency of the contact desired to be detectedand economical merits. As a matter of course, wiring theconstant-voltage power supply 81 and the voltage detector 82 to furnacemembers is considerably easy for a person skilled in the art, as in thecase of connection between the supply-and-exhaust pipe 21 of the cooler19 and the exterior wall surface of the chamber 11. Moreover, the numberand locations of the insulation members 80 to be attached are notlimited to the examples shown in FIG. 18.

Mention will be made here of the embodiment. In reality, contactresistance between the cooler 19 (made of stainless steel) and thethermal insulation member 18 (carbon) was measured to be 10 Ω or less,and contact resistance between metal furnace members (made of stainlesssteel or other metal) was measured to be 10 Ω or less. These resistancevalues are said to constitute substantially internal resistance of acircuit. It is evident that such resistance does not hinder the touchsensor from monitoring contact by means of detecting variations involtage. Cooling water circulates through the cooler 19. When thepresent invention is implemented, resistance of cooling water must betaken into consideration. If resistance of cooling water assumes a valueof 10 kΩ or thereabouts, consideration of potential electricalconduction of cooling water becomes less necessary.

More specifically, the insulation members 80 a and 80 d are to beattached outside the CZ furnace, and hence a commercially-availableinsulation material (e.g., Duracon™ or Delrin™) which is commonly usedand commonly purchased can be adopted as material of the insulationmember 80. In contrast, the insulation members 80 b and 80 c are to bemounted inside the CZ furnace, and hence they should preferably beformed from SiO₂ of high purity.

<Detection of Overload and Anomalous Variation in Weight>

In a common CZ single crystal puller, the single crystal 17 is pulledthrough use of the wire 15, and the wire 15 is taken up by the take-upmachine 16. However, if a load cell attached to the pull head of thetake-up machine 16 or a motor used for driving the take-up machine 16 issusceptible to overload, the CZ single crystal puller equipped with acooler according to the present invention is constructed so as to stopat least the motor 26 a of the hoisting-and-lowering machine 25. If themotor 26 a used for driving the hoisting-and-lowering machine 25 issusceptible to overload, the hoisting-and-lowering machine 25 isconstructed so as to stop at least the motor 26 a. More preferably, whenany of the motors is susceptible to overload, the motor 26 a isimmediately rotated in reverse, thereby retracting the cooler 19 in thereverse direction and thus avoiding occurrence of a serious accident. Ifnecessary, the cooler 19 is moved away from the surface of the siliconmelt 12 or the pulled single crystal 17 at high speed (300 mm/min.), asin the case of the embodiment in which temperature detection iseffected, thus avoiding occurrence of a serious accident.

Detection of overload by a motor can be easily effected by use of only aservo motor, as is obvious for persons skilled in the art.

<Detection of Steam>

The CZ single crystal puller equipped with a cooler according to thepresent invention employs a cooler of water circulation type. Hence, thepuller is equipped with a steam detection device for detecting steamoriginating from the CZ furnace. If the steam detection device hasdetected steam, the detection device acts so as to move the cooler awayfrom the pulled single crystal.

More specifically, the CZ single crystal puller equipped with a cooleraccording to the present embodiment comprises the pressure sensor 31 fortracing variations in the internal pressure of the chamber 11; thetemperature sensor 33 for sensing variations in the temperature of a gaswhich is stored in the chamber 11 and is to be evacuated by the vacuumpump 20; and the infrared-ray sensor 34 for sensing infrared raysabsorbed by the gas which is stored in the chamber 11 and is to beevacuated by the vacuum ump 20. In the event of water leakage arising inthe pipe of the cooler 19, the leaked water is changed into steam by theheat in the furnace, and the steam in turn causes variations intemperature or pressure of the furnace. By means of sensing a change intemperature or pressure in the furnace, water leakage can be sensedaccurately. Since steam absorbs infrared rays, the infrared-ray sensor34 is provided for enhancing the accuracy of detection of water leakageby means of determining absorption of infrared rays.

If any one of the above-described sensors is disposed in the furnace,water leakage can be sensed sufficiently. However, in order to make allpossible preparations for sensing water leakage, a plurality of sensorsmay be disposed in combination. For the same reason, a plurality ofsensors of the same type may also be disposed.

Unless a comparatively large amount of steam is present, the temperaturesensor 33 will fail to distinguish variations in temperature fromchanges in another condition. For this reason, in order to accuratelysense variations in temperature caused by steam, the temperature sensor33 must be disposed at a position where steam concentrates. Basically,the temperature sensor 33 is preferably disposed in an exhaust channel(i.e., a pipe connected to the vacuum pump 20). Since the infrared-raysensor 34 can immediately sense a trace amount of steam, the sensor canbe attached not only in the exhaust channel but anywhere, such as aninterior wall surface of the chamber 11.

The sensors are connected to the controller 35. In the resentembodiment, the pressure sensor 31 is connected directly to thecontroller 35. Further, the temperature sensor 33 is connected to thecontroller 35 by way of a corresponding processor 33 a, and theinfrared-ray sensor 34 is connected to the controller 35 by way of acorresponding processor 34 a.

For example, if a rise in the internal pressure of the chamber 11stemming from generation of steam has been sensed by the presser sensor31, if the temperature sensor 33 has sensed an increase in thetemperature of an exhaust gas resulting from generation of steam, if theinfrared-ray sensor 34 has sensed abnormal absorption of infrared raysin the absorption range of steam, or if several or all of thesesituations have occurred simultaneously, the controller 35 is activated,to thereby illuminate an indicator 36. Further, the controller 35 closesa solenoid valve 37 for regulating inflow of cooling water, thusstopping inflow of cooling water. Simultaneously, another solenoid valve39 which usually remains closed is opened, thereby opening the end ofthe exhaust pipe 21 b to the atmosphere. In the event of occurrence ofwater leakage, leaked water is changed to steam, thus resulting in anincrease in pressure. In this case, cooling water circulating throughthe cooler 19 is discharged to the outside by way of the solenoid valve39, thereby diminishing the amount of water dropping into silicon melt.

The pipe to be released to the atmosphere is also connected to thesupply tube 21 a, and hence cooling water which is about to be suppliedto the cooler 19 can also be discharged. By means of such a tube, in theevent of occurrence of water leakage, the cooling water still remainingin the cooler 19 can be discharged in as great an amount as possible,thus lessening damage which would be inflicted on the CZ single crystalfurnace. Even in such a case, shutdown of the CZ single crystal furnacecan be avoided. In order to make preparations against emergency, thechamber 11 of the CZ single crystal puller according to the presentembodiment is provided with a safety valve 40. Further, check valves 41,42, and 43 are attached to a cooling-water outlet pipe or a non-pressurepipe. Thus, all possible preparations against emergency are taken.

<Others>

In the specification, “anomalies” arising in the CZ single crystalpuller may imply, for example, detection of anomalies caused byoperators, power failures, failures of a vacuum pump, failures of powersupply for a heater, damage to furnace members, failures of acooling-water pump, etc.

If such “anomalies” arise, as shown in FIG. 2, at least the motor 26 aof the hoisting-and-lowering machine 25 is stopped. In some instances,the motor 26 a is quickly rotated in reverse, thereby moving the cooler19 in a reverse direction, thereby preventing occurrence of a moreserious problem which would otherwise arise. Moreover, in order to avoidoccurrence of a serious problem, in the event of occurrence of“anomalies,” a cooler is moved at high speed (300 mm/min.) away fromfurnace members (i.e., the surface of a silicon melt and a singlecrystal) that would be dangerous were the cooler to approach them.

As has been described above, even when a cooler through which coolingwater circulates is disposed within the CZ furnace, the CZ singlecrystal puller according to the present invention accurately preventsnear miss or contact between the cooler and a furnace member or retractsthe cooler by means of detecting the near miss or contact, thuspreventing damage to the cooler. Accordingly, there can be preventedoccurrence of a serious accident, such as an explosion, which wouldotherwise be caused by expansion of cooling water in the cooler.

Further, the cooler is quickly moved away from a substance, such as amelt, which would act as a heat source, or from other dangerouslocations. Hence, in the event of water leakage, there can be diminisheddamage which would otherwise be inflicted by water leakage.

Since the CZ single crystal puller according to the invention enablesquick changing of position of the cooler as well as preparations forsafety, the distance between the cooler and the level of a melt can becontrolled during the course of pulling of a single crystal, asrequired. Thus, further increase in a single-crystal pull rate and animprovement in production efficiency can be implemented.

Even when furnace members are deformed as a result of long-term use,substantially identical requirements can be maintained by means offinely adjusting the distance between a melt surface and a cooler andthe distance between a thermal insulation member and a cooler, thusenabling continuous production of crystal of stable quality.

[Palette (Combination) of Factors Relating to Miniaturization ofCrystalline Imperfections]

The following three methods are effective as measures for miniaturizingcrystalline imperfections during the course of crystal growth throughuse of two or more “factors”in combination.

1) Increasing the rate at which a crystal is to be cooled requires anincrease in the temperature gradient of the crystal and an increase inpull rate. There is provided a method of providing a CZ single crystalpuller equipped with a thermal insulation member for shielding crystalheat radiated from melt or a heater or a cooler for cooling the crystal.

2) A method of miniaturizing defects by means of addition of nitrogen tocrystal during the course of crystal growth (where a defect densityincreases).

3) A method of applying a magnetic field to a growing crystal. When amagnetic field is applied to a crystal during the course of growth,natural convection flows arising in silicon melt in the verticaldirection are suppressed, thereby resulting in an increase in thetemperature gradient of a melt. Consequently, a pull rate is increasedabout 20% or thereabouts over that obtained when no magnetic field isapplied to the crystal during the course of growth, thereby yielding anadvantage of an increase in cooling speed. As has been statedpreviously, oxygen concentration can be controlled over a wide range,thereby yielding an effect of controlling deposition of oxygen whichwould form gettering sites for gettering heavy metals.

As illustrated in an example to be described later, no interference orcancellation arises between disposition of a cooler, application of amagnetic field, and nitrogen doping; rather, an additive or synergisticeffect can be expected. So long as requirements for the CZ singlecrystal puller are set through use of anyone or several of theconditions in combination; that is, disposition of a cooler, nitrogendoping, and application of a magnetic field, sizes of crystalimperfections are controlled, thereby optimizing the characteristics ofa post-heat-treatment wafer.

In connection with these factors, as a result of disposition andadjustment of the thermal insulation member, and adjustment of distancebetween the bottom of the thermal insulation member and the meltsurface, neither interference nor cancellation arises in the dispositionof a cooler and nitrogen doping.

In connection with a magnetic field, ripples in the surface of a meltsurface disappear when a magnetic field is applied to the melt. When amagnetic field is applied to the melt surface, the thermal insulationmember can be moved much closer to the melt surface. As a result of thethermal insulation member being located closer to the melt surface, theeffect of shielding the crystal from heat can be enhanced, therebyincreasing the temperature gradient of the crystal. Such an increase intemperature gradient contributes to miniaturization of crystallineimperfections or an increase in pull rate. Accordingly, in terms of therelationship between the disposition and adjustment of a thermalinsulation member and a magnetic field, it is thought that a positiveresult will be yielded without involvement of a negative result. Hence,in principle, application of a magnetic field can be added to thepalette for miniaturizing crystalline imperfections, along withdisposition of the cooler and nitrogen doping.

In this regard, a method of reducing the sizes of defects by means ofcontrolling a V/G ratio or controlling the diameter of an OSF ring (asdescribed in Japanese Patent Application Laid-Open No. 154095/2000) anda method of reducing the sizes of defects by means of increasing acooling rate of a crystal (as described in Japanese Patent ApplicationLaid-Open No. 208987/1998) encounter difficulty in achieving a coolingrate at which defects can be sufficiently reduced, for reasons of anincrease in thermal capacity associated with an increase in the diameterof a crystal. In the case of use of only the nitrogen doping method,limitations are imposed on the concentration of nitrogen which can bepresent in a crystal. For this reason, if nitrogen is doped in a crystalto high concentration, deposition of oxygen is promoted. Since a DZlayer cannot be ensured, the doping level of nitrogen is limited. Bymeans of appropriate combination of a cooler, nitrogen doping, andapplication of a magnetic field, there can be expected a potentialsolution to a problem which arises when only the cooling speed ofcrystal is increased and a problem which arises when solely nitrogendoping is used.

Embodiments of Crystal Produced by Use of a Cooler

Embodiments of crystal produced by use of a cooler are as follows: TABLE2 1 Cooling rate in a crystalline-imperfection formation temperaturezone is at least 5° C./min. 2 The size of defects arising in a singlecrystal is 110 nm or less. 3 The density of defects arising in a singlecrystal is 5 × 10⁶/cm³ or more. 4 Wafers are produced by means ofsubjecting to heat treatment slices cut off the crystals that have beengrown under the foregoing conditions (a desired wafer can be produced bydetermination of the temperature and time in accordance with anapplication). 5 A wafer which is produced under the foregoing conditionsis characterized in that defects detected by the LST method are 1/cm² orless in density.

Embodiments of Crystal Produced by Use of a Cooler and Nitrogen Doping

Embodiments of crystal produced by use of a cooler and nitrogen dopingare as follows: TABLE 3 1 The size of defects arising in a singlecrystal is 90 nm or less. 2 The density of defects arising in a singlecrystal is 1 × 10⁷/cm³ or more. 3 The concentration of oxygen in asingle crystal is 12 × 10¹⁷ atoms/cm³ or less. 4 Wafers are produced bymeans of subjecting to heat treatment slices cut off from the crystalsthat have been grown under the foregoing conditions (a desired wafer canbe produced by determination of the temperature and time in accordancewith an application). 5 A wafer which is produced under the foregoingconditions is characterized in that defects detected by the LST methodare 1/cm² or less in density.

EXAMPLES

In the present example, there were produced two types of crystalaccording to related-art requirements and requirements for providing acooler in a crystal puller, so as to satisfy the followingspecifications: employment of boron as a dopant, a diameter of 200 mm,p-type, crystal orientation of <100>, and a resistivity of 0 to 10 Ωcm.The relationship between defect density, defect sizes, and nitrogenconcentration was checked with regard to the above two types of crystalwhen nitrogen is added to related-art requirements and when nitrogen isadded to requirements for installing a cooler (FIGS. 20A and 20B).

Further, the relationship between cooling rate, defect density, anddefect size was checked with regard to the above two types of crystalwhen nitrogen is added to related-art requirements and when nitrogen isadded to requirements for installing a cooler (FIGS. 21A and 21B).

Further, mappings of typical LST surfaces and examples of defect densityare also shown (FIG. 23). As a method for evaluating the LST surfaces,there was adopted a method for detecting crystalline imperfections at adepth of about 5 μm in a wafer surface, by means of radiating avisible-light laser (λ690 nm, MO601 produced by Mitsui Mining & SmeltingCo., Ltd.) on the surface of a wafer at an angle, and detecting theresultantly-scattered light through use of a CCD.

In FIG. 20B, it can be seen that miniaturization of crystallineimperfections associated with an increase in the doping level ofnitrogen is accelerated by presence of a cooling member (i.e., acooler). From FIG. 21B, it is understood that miniaturization of crystalimperfections associated with an increase in cooling speed is enhancedin association with an increase in the doping level of nitrogen. Fromthese descriptions, it is understood that at least the effect ofminiaturizing crystalline imperfections yielded by nitrogen doping canbe sustained after disposition of a cooler.

FIG. 22 is a graph showing the influence of application of a magneticfield on crystal growth rate and defect size. In the drawing, histogramsshow defect sizes (see the right-side vertical axis), and a solid squaredenotes a pull rate (the left-side vertical axis).

As shown in FIG. 22, when a magnetic field is applied to a crystal,miniaturization of defects and an increase in pull rate can be achievedsimultaneously.

Therefore, it is understood that application of a magnetic field to acrystal positively affects a pull rate. As has been describedpreviously, the melt surface is quelled by means of application of amagnetic field, and the bottom of the thermal insulation member is movedclose to the melt surface, thus increasing the longitudinal temperaturegradient of the crystal. As a result, it is thought that a pull rate canbe improved. In any event, the pull rate can be actually increased bymeans of application of a magnetic field.

As shown in FIG. 23, a wafer is produced from the crystal which has beenpulled through use of a cooler, by means of heat treatment. Further,another wafer is produced from the crystal which has been pulled throughuse of a cooler and nitrogen doping, by means of heat treatment. It isseen that defects formed in these two wafers are smaller than thoseformed in the wafer produced from a related-art crystal by means of heattreatment. It is understood that the density of defects arising in awafer after annealing is considerably diminished by means of animprovement in a thermal insulation member, use of a cooler, orcombination of a cooler and nitrogen doping. The heat treatmentatmosphere required for effecting annealing can be embodied by anon-oxidizing Ar atmosphere, an He atmosphere, or a mixed gas atmosphereconsisting of hydrogen, Ar, and He.

[A Puller Operating According to a Predetermined Program]

A storage medium having stored therein data such as those shown in thefollowing table 4 is housed in the silicon single crystal pulleraccording to the present invention. On the basis of the data, a siliconsingle crystal is pulled. In the table, data pertaining to factor“Disposition and adjustment of a cooler” are specified as data S-D1 forspeeding up a crystal pull rate. Data pertaining to factor “Adjustmentof a hot zone” are specified as data S-D2 for speeding up a crystal pullrate. Data pertaining to factor “Disposition and adjustment of a thermalinsulation member” are specified as data S-D3 for speeding up a crystalpull rate. Data pertaining to factor “Adjustment of distance between thebottom of the thermal insulation member and the melt surface” arespecified as data S-D4 for speeding up a crystal pull rate. Datapertaining to factor “Application and adjustment of a magnetic field”are specified as data S-D5 for speeding up a crystal pull rate. Thesedata sets are also specified as K-D1, K-D2, K-D3, K-D4, and K-D5 datapertaining to miniaturization of crystalline imperfections. Further, thedata sets are specified as SK-D1, SK-D2, SK-D3, SK-D4, and SK-D5 datapertaining to both speeding up of a crystal pull rate andminiaturization of crystalline imperfections.

Here, data pertaining to factor “Adjustment of Doping Level of Nitrogen”are irrelevant to speeding up of a crystal pull rate. Hence, the dataare not specified as “S-D” or “SK-D.”; the data are specified as merelyK-D6 pertaining to miniaturization of crystalline imperfections.

These data sets basically represent accumulation of data of the past. Ifnecessary, the data may be updated, regardless of whether the data arecomputed values or measured values. TABLE 4 Speedup + SpeedupMiniaturization Miniaturization Factors S-D1 K-D1 SK-D1 Installation andadjustment of a cooler S-D2 K-D2 SK-D2 Adjustment of hot zone S-D3 K-D3SK-D3 Installation and adjustment of thermal insulation member S-D4 K-D4SK-D4 Adjustment of distance between bottom of thermal insulation memberandmelt surface S-D5 K-D5 SK-D5 Application and adjustment of magneticfield K-D6 Adjustment of doping level of nitrogen

As illustrated in the following table, the data correspond to theprogram which controls the factors by reference to the data. The storagemedium having stored therein the data provided in Table 4 and thestorage medium having recorded thereon the program corresponding to thedata shown in Table 4 may be stored in the puller. Alternatively, thestorage mediums may be stored outside the puller and carried for use, asrequired. TABLE 5 Data Corresponding Program Speedup S-D1 S-P1 S-D2 S-P2S-D3 S-P3 S-D4 S-P4 S-D5 S-P5 Miniaturization K-D1 K-P1 K-D2 K-P2 K-D3K-P3 K-D4 K-P4 K-D5 K-P5 K-D6 K-P6 Speedup + Miniaturization SK-D1 SK-P1SK-D2 SK-P2 SK-D3 SK-P3 SK-D4 SK-P4 SK-D5 SK-P5

When the puller according to the present invention is activated, initialdata are loaded into the puller, and an appropriate factor is selectedfrom the data palette shown in Table 5. Here, the data to be initiallyloaded correspond to the size of a crucible, the amount of material tobe charged initially, the length and diameter of a desired crystal, acrystal, and the number of rotations of the crucible.

When an appropriate factor has been selected from the data palette shownin Table 5, a program corresponding to the thus-selected data isstarted, thereby arranging the internal environment of the puller (e.g.,the geometry of a hot zone). A rate at which a single crystal is to bepulled is set to the maximum speed which is assumed to be possible inthe thus-arranged environment. A silicon single crystal is pulled whilefine adjustment is being performed during the course of pullingoperation.

By means of activating the puller, a silicon ingot or silicon wafers canbe produced at a speed higher than that which has been expected thusfar. Many of the thus-produced silicon ingot or wafers involve smallerdefects. Hence, such a silicon ingot or the wafers are suitable for useas wafers for annealing purpose.

By means of the silicon wafer production method according to the presentinvention, there are devised measures for miniaturizing defects whichwould arise and grow in a crystal growth step and measures for effectinghigh-speed pulling of crystal, in order to optimize, by means ofhigh-temperature treatment, a perfect region in a wafer surface which isimportant for determining the characteristic of a device. A great effectcan be yielded by means of use of the measures in combination.

As mentioned previously, perfection of a wafer surface layer can beexpected by means of increasing the temperature of heat treatment orextending the time of heat treatment. However, these methods involveproblems of contamination of a wafer with heavy metals due to anincrease in heat treatment, wafer slippage, and a cost hike resultingfrom extension of the time of heat treatment. In terms of elimination ofthe demerits ascribable to these requirements for heat treatment, thesilicon wafer production method according to the present invention canbe said to yield a great effect.

Further, a device structure can be roughly divided into two types; thatis, a stacked structure and a trench structure. According to the type ofstructure, the depth of a perfect region in a wafer surface layerrequired for a device changes. In terms of optimization of wafer qualityaccording to the application thereof, the silicon wafer productionmethod according to the present invention can be said to be an effectivemethod.

1-27. (canceled)
 28. A Czochralski (CZ) single crystal pulley forpulling a single crystal from a melt, having a crucible for storingmelt, a crucible hoisting-and-lowering apparatus for hoisting orlowering the crucible, a thermal insulation member for surrounding apulled single crystal, a heater for supplying heat to the crucible, acooler for cooling the pulled single crystal, and a cooler movementapparatus for moving the cooler, wherein the cooler movement apparatuschanges a travel speed of the cooler in two or more steps. Preferably,the cooler movement apparatus cooler hoisting-and-lowering apparatus formoving the cooler vertically.
 29. A Czochralski (CZ) single crystalpuller for pulling a single crystal from a melt, having a crucible forstoring melt; a crucible hoisting-and-lowering apparatus for hoisting orlowering the crucible; a thermal insulation member for surrounding apulled single crystal; a heater for supplying heat to the crucible; acooler for cooling the pulled single crystal; a chamber for storing thecrucible, the crucible hoisting-and-lowering apparatus, the thermalinsulation member, the heater, and the cooler; and a cooler movementapparatus for moving the cooler, wherein the cooler includes a coolingpipe stack which surrounds a pulled single crystal, and asupply-and-exhaust pipe which passes through the chamber and suppliescooling water to the cooling pipe stack, and the cooler movementapparatus includes a bridging member connected to the supply-and-exhaustpipe, a screw-threaded shaft screwed to the bridging member, and a drivemember for rotating the screw-threaded shaft.
 30. The CZ single crystalpuller as defined in claim 29 further comprises anexpansion-and-contraction member which covers an area in the chamberthrough which the supply-and-exhaust pipe of the chamber passes suchthat a hermetic state in the chamber is maintained, and expands orcontracts in accordance with vertical movement of the supply-and-exhaustpipe, a screw-threaded shaft screwed to the bridging member, and a drivemember for rotating the screw-threaded.
 31. The CZ single crystal pulleras defined in claim 30 characterized in that the coolerhoisting-and-lowering apparatus moves the cooler in the verticaldirection.
 32. The CZ single crystal puller as defined in claim 30 ischaracterized in that the cooler hoisting-and-lowering apparatus 5 movesthe cooler in an inclined direction.
 33. The CZ single crystal puller asdefined in claim 32 characterized in that a plurality of pieces ofcooler hoisting-and-lowering apparatus are provided in the chamber andthat the cooling pipe stack of the cooler is separated into 10 separatedinto segments which are to be integrated so as to constitute acylindrical shape and is equal in number to the coolerhoisting-and-lowering apparatus.
 34. The CZ single crystal puller asdefined in claim 31 further comprises an encoder for tracing a distanceover which the cooler is vertically moved.
 35. The CZ single crystalpuller as defined in claim 29 further comprises a limiter member forhindering lower movement of the bridging member from a predeterminedposition of the screw-threaded shaft, said limiter member being a solidmember formed from a limiter switch.
 36. The CZ single crystal puller asin claim 29, the cooler hoisting-and-lowering apparatus changes thespeed of vertical movement of the cooler in two steps or more.